Two situations need a little care when a template experiment is live: switching your theme, and running across Shopify Markets.
Switching or publishing a new theme
You can change your live theme while an experiment is running — but because Cooee reads alternate templates from your live theme, the alternate template must exist in whatever theme is live.
Before you publish a new theme, make sure it contains:
The alternate template you're testing — for example
templates/product.daypack.json. If you built the new theme from an older duplicate, templates created afterwards may be missing.The Cooee app embed, enabled in the new theme (Online Store › Themes › Customize › App embeds). Without it, Cooee's runtime doesn't load and no experiments run.
If the alternate template is missing from the newly-published theme, Shopify falls back to the default template — so variant visitors quietly see the control and the experiment stops producing a real comparison. Recreate the alternate template in the live theme to restore it.
Recommended: add the alternate template to the new theme before you publish it, and confirm the Cooee app embed is on. Then publish.
Shopify Markets
Template experiments work with Shopify Markets — including market domains, subdomains, and URL-path routing — as long as the markets are served by the same theme. Assignment and the ?view= parameter are preserved across the market routes.
One thing to plan for: market-specific (contextual) customisations are not copied to your alternate template automatically. If you use Shopify's per-market template customisations — different copy, imagery, or layout for a country — you'll need to recreate those customisations on the alternate template as well, or that market's variant visitors won't see the localised version.
As long as the alternate template exists in the theme serving a given market, visitors in that market are included in the experiment normally.