Can Asuswrt-Merlin remap a LAN port to function as a WAN port?

I'm currently using TomatoUSB on my RT-N16 router because my WAN port is dead and I needed to remap the one of the LAN ports to a WAN port.

Is this something that's possible with the Asuswrt-Merlin firmware? I'd like to switch firmwares since I'm unable to get the correct speeds with Tomato.

Any information or help would be appreciated. Thanks!