Quilt is a system for managing changes to source code. To quote from the RPM package:

These scripts allow one to manage a series of patches by keeping track of the changes each patch makes. Patches can be applied, un-applied, refreshed, etc.

I've played with quilt and it worked out nicely. Notably, it has very useful support for easily adding more patches to an RPM (which is already a base program version plus a stack of patches).

Quilt is installed on gpu; see quilt(1) for the man page and /usr/share/doc/quilt-0.40/quilt.pdf for a PDF paper on using it.