Don't Revert to checkout.liquid

I have one dev store. I have a feature that is about to be launched and requires changes to the code in the checkout.liquid file. Currently, my store is using Checkout customization, but there is no way to disable it to use the code in checkout.liquid.

This is an image of another store that can disable Checkout customization. I don’t know what settings I’m missing.

Checkout.liquid can be enabled only for Shopify Plus stores by Shopify support team on request at the moment. Shopify is trying to avoid enabling checkout.liquid because this feature will be retired in August 2014.