How do you rebuild and apply a portion of the kernel?

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http://askubuntu.com – I was following the steps here to build my own kernel, which worked great, then I wanted to make a small tweak to the setup file (/arch/x86/kernel/setup.c) and rebuild it to see my message printed in the dmesg log. Before I clean and build again, is there a way to avoid the delay this will have? Can I just rebuild a portion of the kernel that I changed or do I really have to clean/rebuild the entire thing? (HowTos)