Customising the Shopify Horizon Theme Without Losing Your Changes on the Next Update

Your Horizon theme has had another update. The banner in the theme editor looks helpful. Then you notice the custom product badge is gone, the colour palette has reset, or the snippet your developer added last month has quietly disappeared.

If you installed one of Shopify's Horizon themes (Fabric, Ritual, Vessel or any of the other presets built on the same base), you are not imagining it. Shopify Horizon theme customisation works differently from what most store owners learned on Dawn, and the update cadence is much faster. This article covers which changes survive an update, which don't, and how to customise Horizon without rebuilding your work every few weeks.

Why Horizon theme updates overwrite changes more often than Dawn did

Dawn was a slow-moving theme. Plenty of stores edited its code once, ignored updates for a year and got away with it. Horizon is different. Since launching in May 2025 it has shipped a steady run of minor versions. Third-party changelogs record five minor releases between October 2025 and June 2026. The June 4.1.1 release replaced the colour system, and merchants reported lost palette settings and custom code wiped after updating.

The reviews reflect that. As of July 2026, Horizon sat at roughly 35% positive across 190 reviews on the Theme Store, with updates overwriting customisations the most common complaint. In fairness, Dawn scores about the same, so part of this is how Shopify's percentage-based ratings work. But the pattern in the Horizon reviews is clear: people are losing work.

The mechanism is simple. Shopify's theme update documentation says a theme only updates automatically when every file, apart from settings_data.json and the JSON templates, is in its original state. Touch one Liquid file in 'Edit code' and your store drops out of automatic updates. From then on, each update arrives as a new theme copy in your library that you apply by hand. Your old theme stays put with your edits inside it, but the new copy is built from Shopify's files, not yours.

Which Horizon theme customisations survive an update

Not everything is at risk. Here is the honest breakdown, based on how Shopify handles updates and what we see on client stores.

Theme settings (survive). Colours, typography, spacing and layout choices made in the theme editor are stored in settings_data.json and carry across. The June 2026 colour system change was the exception that proves the rule: when Shopify restructures a setting, the old value has nowhere to go.Section and block content (mostly survive). Your homepage sections, product page blocks and their settings live in JSON templates, which Shopify preserves. Where a section has been renamed or restructured in the new version, you may need to re-add it.App blocks and app embeds (survive). Apps added through the theme editor sit in template JSON and settings, not in theme code. They come across cleanly.Metafields and metaobjects (survive). Data stored in metafields is attached to your products, not your theme. Any Horizon block that reads a metafield keeps working.Custom Liquid and custom CSS boxes (survive). Code typed into Horizon's built-in custom Liquid block, or into a section's custom CSS field, is stored as settings. A member of Shopify's Horizon team recommended exactly this on the community forum: stick to custom Liquid blocks so you are not porting code by hand on every update.Edits to Horizon's own files (do not survive). Changes to theme.liquid, the core files in the blocks folder, the base stylesheet or any shipped snippet are overwritten. An asset you added with a filename that collides with a Shopify file is also at risk.New files you added (usually survive, with a catch). A new section or snippet with a unique name is not part of Shopify's update, so nothing overwrites it. But it only renders if something still calls it, and the thing calling it is often theme.liquid, which is a vendor file.

The safe way to customise the Horizon theme

Shopify's own growth services team has published a guide on customising Horizon while keeping it upgradable, which tells you how common the problem is. Their advice lines up with how we build. The short version is an order of preference:

Theme settings first. If a setting exists for it, use it. A surprising number of 'we need custom code' requests on Horizon turn out to be a setting nobody had found.Blocks, app blocks and metafields second. Horizon's block architecture is far more flexible than Dawn's. Most layout changes a merchant wants can be done by rearranging or nesting blocks, pulling in a metafield, or adding an app block.Custom Liquid and custom CSS boxes third. Scoped to a section, saved as data, and they survive updates.New, clearly named files fourth. If you genuinely need a new section or snippet, add it as a new file with an obvious prefix (your brand name works). Never edit a shipped file to do the same job.One injection point only. If custom code must be referenced from theme.liquid, keep it to a single render call to one snippet you own. When an update lands, you re-add one line, not twenty.

The last two points are what separate a store that updates in an hour from one that takes a developer two days. Keep an unmodified copy of the upstream theme in your library, and if you work with a developer, ask them to keep custom work in version control alongside an untouched Horizon branch. Diffing the two tells you exactly what needs reapplying.

Before you press update

Duplicate the live theme first. Always.Apply the update to the unpublished copy and check the pages that matter: home, a collection, a product with your custom blocks, cart and checkout.Compare your settings and custom files against the old copy.Only then publish, and keep the previous theme in your library for at least a couple of weeks.

Dawn vs Horizon: the realistic cost of migrating

If you are still on Dawn or another Online Store 2.0 theme, be clear-eyed about what moving to Horizon involves. There is no migration tool. Shopify staff have said as much on the community forum, and they have also said Dawn remains fully supported. Horizon's section and block model is a rebuild, not an upgrade, so every template, section and customisation has to be recreated.

In practice we see three bands of effort. A lightly customised Dawn store with standard sections can be rebuilt on a Horizon preset in a few days of senior time. A store with custom sections, a handful of apps wired into the theme and a few years of accumulated code edits is more like 2-4 weeks, because each piece of custom code has to be rethought in Horizon's block model rather than copied over. A heavily customised store should treat the move as a theme build project in its own right.

One more caution: a theme migration is a conversion event. Layouts shift, trust signals move and your product page changes. Treat it the way you would any redesign, with a baseline measured before and after. We cover that decision in more depth in when to redesign versus optimise your Shopify theme.

When a custom build still beats a Horizon preset

Horizon is a good base for many stores, and we build on it. But a preset is a starting point, not a strategy. There are three situations where a custom theme build, or a deliberately forked Horizon, is still the better call:

Your product page needs logic the block model cannot express: configurators, bundles with conditional pricing, B2B rules, or content that varies by market.You have measured conversion problems and need to test layouts quickly. A theme you fully control is easier to experiment on than one you are trying to keep update-compatible.You are doing enough revenue that a two-day scramble after every Horizon update is a real cost. At that point, forking the theme, owning it and updating on your own schedule is often cheaper than chasing upstream.

Forking has a price: you give up automatic updates and take on security and accessibility patches yourself. That is a fair trade for a store doing serious volume with a developer on hand, and a bad one without. Our Shopify theme design and development work covers both routes, and we will tell you which one fits before any build starts.

The question behind the question

Most of the Horizon customisation requests we get from UK brands are not really about the theme. They are about conversion. The store has traffic and the product sells, but the rate at which visitors become customers has flattened. Moving a section feels like action, but without measurement it is guesswork wrapped in Liquid.

Most Shopify brands don't have a traffic problem. They have a conversion problem. The theme is only one of the levers.

Before you spend a week rebuilding on a Horizon preset, it is worth knowing which page, which device and which step is actually losing you money. That is where our conversion rate optimisation work begins, and it is the whole premise of the Conversion Growth Retainer: theme changes are one tool among several, each one tested rather than assumed.

The takeaway

Customise Horizon through settings, blocks, metafields and custom Liquid boxes. Keep any real code in your own clearly named files with a single hook into theme.liquid. Always update on a duplicate. Do that and Horizon's fast update cycle stops being a threat and becomes what it should be: free improvements every few weeks.

If your store has outgrown what a preset can do, or an update has already cost you work you cannot get back, talk to us. We are a senior Shopify team in Glasgow, 12 years in, working with brands across Scotland, the UK and beyond. You will get a straight answer on whether you need a fix, a fork or a rebuild.