[CentOS] rpm - diff and patch updating

I am attempting to create a rpm of the latest version of a program.  The
rpm for the previous version contains a number of patch files that make
numerous changes various files in the tar.gz as downloaded from the
project's website so it will work properly on Linux.

The latest version of the program has changed enough stuff that some of
the patches now fail to apply.  "1 out of 1 hunk FAILED" and so on.
Upon comparing the previous version's files to the latest version, I see
that the problem is that some of the files that need to be patched have
had some stuff moved around a bit, just enough to (apparently) cause
patch to fail.

By way of experimentation, I manually changed one of the files in the
new version to match what the patch says it should be, then created a
new patch file from that and it applies and appears to work fine.  (I
patched the previous version's file, compared the result to the original
and made the same change in the new version's file.)

This method seems to work fine when the change is only one or two lines,
but some of the patches are somewhat more involved than that.

It seems to me that there may be an automated way to handle this matter
by somehow patching a into b, then compare a and b and make
corresponding changes in c.  Basically the same process that I just
tried manually on a small patch file, without all of the labour and
chance of a screw-up that would be involved in manually comparing the
old files and rewriting the new file.

I have two questions:

First, am I going about this the right way?  And if so, is there a way
to automate the process as described in the previous paragraph?

Second, what is the proper convention for handling this in a rpm?  The
obvious solution seems to be to create new patch files and throw the old
ones away, then build the rpm from that.  Some of these patches appear
to go back several versions, though, so is there a better or more proper
way to handle this than just throwing them out and making a whole new
set of patches?

I have learned a lot more about patch and diff tonight than I ever
needed to know before.  Very cool stuff, and very useful.
-- 
MELVILLE THEATRE ~ Melville Sask ~ http://www.melvilletheatre.com