Assign WAN/LAN ports on a MR2200 router in a Synology mesh network

I would like to be able to assign the WAN/LAN ports to the guest network on a remotely mounted Synology MR2200AC router that is part of a mesh network consisting of a RT2600 or a RT6600 main router.

My application is a vacation rental where I have the main router locked in a closet, but the MR2200 needs to be in a location that is hard to lock up. I would like to setup a TV and wire it to the assigned guest LAN port. I do not want a visitor to be able to connect to the unlocked/accessible MR2200 with an ethernet cable and get onto the primary network (which is something I think I should prevent).

I am willing to use two RT2600 or RT6600 routers if necessary to do this.