You cannot change that state, you can change the presence state, or maybe the DND state, but not the registered state (grayed out button).
Here is the user event needed to change presence state:
Action: UserEvent
UserEvent: FOP2ASTDB
Family: fop2state
Channel: SIP/606
Value: Break
At the same time you must set that state in the astdb if you want it to be persistent:
/fop2state/SIP/606 : Break
The best way to play with your custom states is to start fop2_server in debug mode level 15
/usr/local/fop2/fop2_server -X 15
Best regards,