The most common Shopify rescue job I get goes like this: the store owner (or a previous developer) edited the theme code years ago, the theme now has an update with fixes they need, and nobody dares click the button. Customizing a theme is fine. Customizing it in a way that makes every update a gamble is what costs money later. Here is how I approach it.
What actually happens when you update a theme
Shopify’s own documentation is clear on this. Anything you changed in the theme editor, such as settings, page layouts, section and block content, new templates and app embed settings, is copied over to the updated theme. Edits made in the code editor are included only if they don’t conflict with the update. After an update, the theme card tells you either that your code edits were successfully included or that they could not be included, and in the second case you have to copy them across yourself. Shopify also says that changes to files in the Templates folder and to settings_data.json are not covered by the code-edit carry-over.
Two other details matter. Updates arrive as a new draft theme, so you can review it before anything goes live. And only themes installed from the Shopify Theme Store receive updates this way. A theme uploaded from elsewhere, or a theme from a third-party designer, depends on that designer to ship updates.
Use the theme editor first
Before touching code, check whether the theme editor can do the job. Colors, fonts, spacing, header and footer layout, homepage sections, announcement bars and most button styles are settings. Because the editor’s changes carry over on update, this is the safest place for any change. Many themes also include a custom CSS box in the theme settings or on individual sections, which is a good home for small visual tweaks.
Add apps through app blocks and app embeds
Apps can attach to a theme in two ways that don’t require code edits. App blocks sit in a specific spot, such as a reviews widget on a product page, and you place them from the Apps section of the block picker. App embeds float over the page or run quietly in the background, like a chat bubble or an analytics script, and you switch them on from the App embeds panel. Shopify notes that some apps still inject code directly into the theme and ask you to paste snippets, and where the theme has a Custom Liquid section you can often paste the code there instead. Also worth knowing: if you change your published theme, apps are not active in the new one by default, so you have to reactivate them.
When you do need to edit code
Sometimes a change really does need Liquid or JavaScript: a custom product template, a bespoke section, a different cart behavior. When that happens I follow a few rules:
- Work on a duplicate. Duplicate the live theme, make and test the change there, and publish only when it works.
- Prefer new files over edits. A new section or snippet file is much less likely to collide with an update than a change inside the theme’s core files.
- Keep changes small and contained. Avoid altering a section’s schema, such as block limits or placement rules, because Shopify warns that schema changes can cause an update to fail.
- Comment and record every edit. Note the file, the date and the reason, so the change can be reapplied in minutes later.
- Save a copy of your customized code before updating. Shopify recommends this too, and a file-comparison tool helps you see exactly what you changed.
A safe way to update
- Read the release notes so you know what is changing.
- Choose the option to add the update as a draft theme. This does not touch your live store.
- Check the card for whether your code edits were included. If not, reapply them from your notes.
- Test the draft: homepage, a collection, a product page, the cart, checkout entry, and any app-powered feature. Check it on a phone as well.
- Publish when it passes, and reactivate any app embeds that did not carry across.
Signs it is time for help
If your store is on an old theme that no longer receives updates, if the theme card keeps saying your code edits could not be included, or if nobody can say what was changed in the code and why, it is cheaper to sort it out deliberately than to wait for a checkout bug. Cleaning up a heavily edited theme usually means moving real needs into theme settings, apps or a small set of well-documented custom files. The same discipline applies to routine upkeep, which I cover in my article on what site maintenance actually requires.
I customize and repair Shopify themes for US and UK stores, including update-safe changes, speed work and accessibility fixes. See my Shopify services, or get in touch and tell me what your store needs.
