Modify linux I/O schedulers

For a project i need to modify Linux i/o schedulers (for example add a few lines to them.)
is there any tutorial available to help me do that?
i/o schedulers are in which files in kernel?
is it enough to just edit that files?
how i can compile modified schedulers? do i need to compile whole kernel or can i replace compiled schedulers in working kernel.
there's 4 schedulers in kernel which can be switched at run time how i can add another scheduler so it also can be used at run time?
thanks in advance