[CentOS] How do I build a modified rpm (Another newbie question)?

Thu Feb 22 18:19:37 UTC 2007
Mark Hull-Richter <mhull-richter at datallegro.com>

I made a minor change to the XFS package (in the unpacked source files),
but I can't figure out which rpmbuild option to use to build from that
changed source file (instead of re-unpacking all the source files,
overwriting all the source files, etc.).

Please assist/explain.

Thanks.