I've never heard of anyone trying to downgrade kernels, but I think it can be done. You're out of luck for proffesional help (fedora is help-free). The best bet is to join the fedora mailing list. Find someone who can help. Thats it.
Is it possible to "downgrade" kernels. I've installed Fedora Core 3: the 2.6.9 kernel included "breaks" one of my applications. Is it possible to install a kernel rpm for Fedora Core 2, which is 2.6.7, or other kernels?