From my experiment (vers 4.1.85) it seem that AP keep in his NVRAM (lwapp_ap.cfg) some values which include the radio setting. Suppose somebody do a bad changes, like activating RRM for a particular radio, it can erase all the fixed values for all the AP in a few seconds.
From what I can see, I don't think controller backup could help in anything for restoring those values. AP will bring with him his NVRAM values. My only thought is to create many AP-Template having my fixed values and to be prepare to run them as restoring backup for AP !
Am I wrong and something easier exist ?