Products are "only" sold through Offers. This construct gives us 2 things. The first is a way to sell multiple products as a bundle and the second is to sell products at different price points, ie different licesnes for software. So if a product is not in an Offer it is not on slae and does not appear in the product list.

"I've made a lot of customizations, so I don't want to run into compatibility issues if I upgrade..."

No, you have forked the code. I always advise against doing that because there is no solution. You cannnot upgrade without losing your changes.

If you are a really good developer you could clone the feature making your own custom fork of just the feature and then you would still be able to upgrade the core and included features and be able to move forward customizing your clone.

Best,

Joe