Hi Fullback,
If you read /opt/etc/rc.local (with cat) you should see that KFurge has added a section:
# Poke holes in the firewall for certain applications
with
/opt/etc/init.kc/iptables_mldonkey.sh
So, I think it would be wise to edit that one in stead of rc.local. But, if you want to stay on the safe side, you'd better edit rc.local, because you can easily recover from a problem with it.
Now, for the edit part, if you have searched this forum you will have come across nano or joe. Use one of these. (ipkg install nano, etc)
Regards,
Marc