You can try, if it's the only l2tp connection originated by the router.
Mangle output and srcnat chains are at your service.
But I don't see in what way is it simpler.
Yeah, so I went with the null-bridge method, it works!
Basically, I created a null-bridge, then in IP>Address List I added a non-existent network IP and a single static IP, and used said IP for the LT2P client.
1. I used "lookup" instead of "lookup only" in IP>Routes to give it redundancy/failover which works relatively well but not that "fast" in switching between the available tables, it takes some time, any workarounds?
2. But how does this null-bridge/non-existent network/static address work though? I would like to understand it fundamentally.
3. Also, I set the VPN client as "WAN" instead of "LAN" in their interface list to get treated accordingly by the firewall filters, that's logical, right?