Do you have remote access to the devices?
If you do you could change the configuration via the web interface or Telnet/SSH or even SMS if you set it up.
Simply set the router to reboot in 20 minutes with
Then set your new apn
"modemcc 0 apn MyNewAPN"
Then tell the modem (not the router) to restart
Now you wait to see if it comes online with the new APN.
If it does, log back in and do
"config 0 save"
If it does not, wait 20 minutes and the router will reboot back to the old config.