To make a modified kernels, assuming some path names, and I use csh(1):
cd /usr/src/sys/arch/sparc/conf
cp GENERIC MYKERN
vi MYKERN # or emacs, or ed, or ... ;edit configuration to suit.
config -s /usr/src/sys -b /var/obj/sys/arch/sparc/compile/MYKERN MYKERN
cd /var/obj/sys/arch/sparc/compile/MYKERN # I keep objects here.
(make depend; make)>&! /var/tmp/make.MYKERN< /dev/null
# if the compile (make) succeeded,
# you should now have a new ./netbsd
# so you can ...
cp netbsd /netbsd.new
shutdown -h now 'test new kernel'
# from the "ok " prompt of the Sun OpenBoot PROM:
boot -s netbsd.new
# the "-s" for single user mode,
# to make sure the kernel can get you to a shell; from there:
fsck / # if you got a clean shutdown, this is unnecessary.
mount / # this you have to do, since root comes up read-only.
mv netbsd netbsd.old
mv netbsd.new netbsd
reboot
# you have the old kernel in case something goes wrong;
# the reboot from this point should bring the system up
# in multi-user mode running the new kernel.
Does this help?