I really want to be able to turn the control surfaces on and off - that would be really useful for making planes with turrets. Right now I have to either make turrets controlled by VTOL/Trim, which are pain to aim, or to make ugly and ineffective control surfaces with hinges/rotators.
yeah what @Feanor said you can already do this
In the xml file of your aircraft, add ( activationGroup="1" ) behind the (maxDeflectionDegree="35" )