Let's assume we would like to add some rules:
iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADEI can use the comment match and add a comment to this line:
iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE -m comment --comment "SOME_COMMENT"
Now, cleaning all the relevant rules in a simple command would be:
# iptables-save | grep -v SOME_COMMENT | iptables-restore
Probably not the best way to do it, but it's simple and fast.