You can add throttle to do landings and touch and goes, drop bombs, have retracts. You can have any mechanical set-up you can imagine except I think it has to be activated through the control lines. Check the AMA rule book for that.
Throttle is/was accomplished through a third line. I'm hearing that some are sending digital pulses through the lines like an RC unit except it is transmitted through the control lines instead of through an antenna.
Lots of possibilities.

Note that this is only from reading about them. Perhaps someone will jump in who actually participated in that event.

George