WAN --> Normal LAN if SFP is in use?

Hey!

I would very much like to upgrade my Old Skool UDMB to the new Dream Router 7. If I buy the RJ-45 --> SFP adapter and use that as the WAN port from my cable modem, is it possible to reconfigure the "dedicated" RJ-45 WAN port into just an additional LAN port?

Thank you!

M.