Actually, testing this further, it doesn't work. You can change the setting on the satellites, and it gets changed back, presumably by the main router. This may not be affecting other people, but is...

@worldofchico Okay, what's working for me, is to telnet to all three routers, and modify /etc/config/wifi, as described above, eg to change the section where it says config backhaul 'backhaul' option...

@ahambou Hi, about this change to /etc/config/wifi I've upgraded to the beta config on my 3 P9s, and I can telnet to all three of them. I can edit /etc/config/wifi, using vi, and save it, can confirm...