Switching WAN provider - transfer given firewall rules to new interface used

[OmnomBánhmì]

There's an ISP change coming up for us, on a multi WAN setup. So atm we have both VDSL (WAN1) and fibre-with-copper (WAN2) active. Coming up will be the fibre-with-copper to be replaced by a fibre connection that does not use copper on the last 50cm of a legacy cabling installation. 

There's no rush with the new setup, because all three shall continue to run in parallel for weeks or even months, and this DEC740 has enough ports for all of it. I'll stick to one aspect of the changes.

From what I've gathered I now have a full setup of WAN interfaces, and a range of firewall rules and such for WAN2. When the new ISP will offer IP it'll connect via interface ax1 - do I have to rebuild everything for the new WAN?

Maybe there is an easy way to copy over given firewall rules to the new interface? It would at least be convenient to be able to do that.

Any pointers appreciated.