You purchase a product.
You customize it.
You customize it some more.
You keep tinkering and tweaking until there is nothing left of the original save for your customizations.
You now have a mess of an upgrade on your hands.
You now have time spent figuring out why you had to customize it to the nth degree.
If you’re having to customize something you bought that much, it might be a sign, you need to build it.
Either that or document everything you do from Day 1 (and we know how that works).