Hmm... I don't really understand what you want.
Are you interested in adding a new Linux kernel source tree to your system, and then compiling and installing the new kernel? Or do you just want to modify and install an existing kernel?
Either way /usr/src/linux will be a symbolic link to your current kernel source tree, which may or may not need to be broken (depending on whether you're installing new source or not).
A good HOWTO on kernel compilation/recompilation/installation exists
here.
If you need more information, please clarify exactly what you are trying to do.
Cheers
ZB