Good news. CP Contact Center send document yesterday. I think this will work without downgrade of FW.

https://knowledgebase.cradlepoint.com/articles/Support/fw6-Change-the-LAN-WAN-Ethernet-Port-Mode-of-a-Cradlepoint-with-Multiple-Ethernet-Ports?retURL=%2Fapex%2FknowledgeSearch%3Fc%3DAll_Products%26k%3Dethernet%2Bport%26lang%3Den_US&popup=false&c=All_Products&lang=en_US