Enable Servo At Altitude

Is there a way to send a command or parameter to the pixhawk to enable a servo at a certain altitude? What language and what software would I need to download to do this? I have mission planner, mavlink and mavproxy. Can you direct me to an example where someone has done this before? I know i can do this in the mission area but I don’t want to run missions just want it to run every time i reach the altitude.

Thank You