Use external kernel source
Add the following lines to local.conf file.
INHERIT += "externalsrc"
EXTERNALSRC:pn-linux-raspberrypi = "/path/to/linux-kernel"
Add extra tasks in recipe file
do_reloc_what_you_want() {
// specific jobs
}
addtask reloc_what_you_want before do_configure after do_prepare_recipe_sysroot