How to insert code block onto the Order Status/ Thank You Check Out Page without Checkout Extension

Hello,

We are in the final stages of getting our subscription app approved by Shopify for the app store. An issue we keep failing on is that we need to add a button that links to our custom customer portal so a customer can edit their subscription after checkout via both the Order Status page, and the Thank you page.

We have this functionality working perfectly using the Checkout out extension.

We are failing this however, because this extension is still in beta, there can and will be shops that wont have access to the extension at all.

I know that there is a drop in in the checkout settings that allows a merchant to copy paste markdown that will edit the Order Status page. However we can not give every single merchant who downloads our app a chunk of code to copy/paste. We need to do this programactically.

I am having trouble figuring out how to go about this. Any help would be much appreciated. Thank you.