Hope this helps, I've been googling for a while but I found some info
"with the truck jacked up, the fox wrench that comes with coil overs is junk. May be good for a few turns but will bend eventually. I was forced to use channel locks (yes they boogered up the ring) but honestly don't know that there is a real tool for this type of preload ring anyway. Once the coilover is installed and while truck is still jacked, only then can you adjust. Spray some pb blaster round the ring/threads. Loosen the Allen (maybe 1/16th inch gap) and then try turning the ring. Hopefully only down as up is much harder."
"I am not sure which way you are adjusting, but I called Fox to ask about adjustments. The installation guide has steps to adjust the height while unloaded and installed on the truck. The tech rep stated that 4 full turns on the collar equals 1/2" in ride height adjustment. "
BUT DONT GET TOO EXCITED BECAUSE.....
http://www.ramforum.com/f40/questions_those_fox_2_0_coilovers-86764/
WHICH WILL LEAD YOU HERE
https://www.f150forum.com/f38/fox-2-0-adjustment-must-read-if-you-have-considering-these-323518/
It looks like it is possible BUT you may strip out the collar doing so and it is recommended to use a spring compressor.