Hi
Well, we had the same prob, ipforwarding stopped after an ip-change occured.
Basically the solution to this is rather simple. When you change a forwarding rule the event remoteacces-update will be signaled, which builds a new masq file under /etc/rc.d. Unfortunately the external ip in the forwarding rule is hard coded in that file. So when an ip-change occurs, the masq file will be read again, but still has the old ip in it. What you need to do is, to trigger the recreation of the masq file with your new ip address.
We accomplished that by creating a symlink in /etc/e-smith/events/ip-change to /etc/e-smith/actions/conf-masq. Make sure that this will be executed before the restart-masq script. (Or you can just copy the link from remoteaccess-update and adjust the linkname so it will be processed just before the restart-masq).
I hope, this information will be useful.
Hanno Stockhausen