Best methodology to customize core?

nopCommerce is awesome, but I have a client that really wants to make some changes to the core code set.  Meaning, they aren't changes I can make in a plugin.

Have you guys had any success with making changes to the core and maintaining it over the long run?  How should I go about it in such a way that when I upgrade I don't lose my changes or such that I can re-apply them as much as possible?

I was thinking about putting the whole solution into source control, and then merging in the changes from the released versions... but it seems like that could get a little tricky.  But I  don't have any other ideas at the moment.

Feedback? Suggestions?

Hi John,

I think source control is your best bet. Perhaps with a little bit of documentation? Anyway, the moment that you start changing core means you need extra overhead in managing the changes. :P

Let's see what others have to say! :D

Source Control and documentation is always the best route to go over keeping track of what changes you made.  I've faced the same issue and find it annoying but that's how it goes when you make core code changes and still do upgrades.  Not sure that there are many other options out there aside from them.