Hey @Brecht 
- I’m not exactly sure which notification template you’re looking for, but if it’s something like the Customer Welcome Email which by default prompts users to login and visit the site, you can modify that template like this in the Admin:
https://admin.shopify.com/store/shop-name-here/email_templates/customer_account_welcome/edit
Other email templates should be able to be found in the general https://admin.shopify.com/store/shop-name-here/email_templates/ menu.
Let me know if we can help out further - if you’re able to share a screenshot of what the email looks like if the above doesn’t help I can see if we’re able to track down where that template might live.