Is it possible to change the elevator's plane?

Hi,I have a project which is to make a few tests.
I want to make automatic plane’s climbing flights. Each one with a different rate climing with a fixed motor power.
I need is the command to modify the elevator in order to modify the climb rate of my plane within modifying motor power. From what I understand, it’s only possible to use NAV- command to modify my plane’s position whereas I want a complete control on the plane.
I know that it’s possible to set SERVO motors values with DO commands but only for auxiliary functions which do not affect the vehicle’s position.
I’m using the autopilot PX4 ,ardupilot, drinekit, jsbsim, and mission planner to record my mission.
If someone could help me, thanks !