Building rpm packages question

[Shane Dawalt <shane dawalt wright edu>]

 I've been building a few source rpms and playing around with .spec 
files.  But the rpm building process leads me down roads I'd rather not 
walk.  For example, I have attempted to build several source rpms that 
have certain features I simply won't use.  These features require 
certain packages (mysql-devel, php-devel, etc.) that I don't want nor 
care about.  I simply see no reason to build these parts of the rpm nor 
install the dependent packages.  Is there some way to influence rpmbuild 
to build only certain packages within a source rpm so that these 
dependencies are not needed?  If not then is there a recommended way to 
tweak the build process short of modifying the spec file?

 And this seems to bring up a question with upgrading the package whose 
spec file is modified.  How is a modified spec file merged with the spec 
file from a newer package?   By hand, I would guess?

 Shane