downlaod the src.rpm. Install the src.rpm. Modify the specfile to indicate that it's a custom kernel in the rpm name. edit the config files in the source directory to reflect your required changes. Then run rpmbuild -ba kernel.spec.
For the name modification, I add something to the end of the "%define release" line. In this case, it might be "4kstack".
I found it necessary to specify the target when building, to get the right arch:
rpmbuild --target i686-linux -ba kernel-2.6-4kstack.spec
(I had to do this to get my legacy PTY's back.)
