how to bring the board back to normal

ok I altered /etc/init.d/rcs on my board to start an application on startup
but now it won't start and so I can't change that file back. What can I do
to fix it.
if it changes anything I have a backup of the original rcs file on my
laptop.

Read kernel's command line documentation in
"Documentation/kernel-parameters.txt", command "init=".