The easiest way to change the text used by various Jilt notification features, like the Post-checkout registration or Capture email on add to cart, is with the Say What? plugin.
Once Say What? is installed, we can go to Tools -> Text Changes in the WordPress admin to make our changes:
From the app's Text Changes page, click the Add New button.
A new Text changes page will load where we'll enter the details of the text we're changing, along with the new customized string.
The original string field must match the string exactly the way it is in the plugin or .pot file in order to modify it. As this can be a bit tricky, we recommend checking out the .pot file to see what the original string contains. We also review customizing specific notifications in these articles: Jilt for WooCommerce notifications and Jilt for EDD notifications.
The text domain will be either jilt-for-woocommerce or jilt-for-edd, depending on which plugin you have installed.
Don't forget to click Add when you're done with your customizations. Test out a notification on your storefront to make sure it's displaying as expected. And if you run into any questions, please let us know.