For those that have external FCU hardware, you can control and set the target altitude with the following simulation events, which are common in most default aircraft.
To display target ALT: AUTOPILOT ALTITUDE LOCK VAR
To increment: Send AP_ALT_VAR_INC100
To decrement: Send AP_ALT_VAR_DEC100
(You can also use …DEC1000 and …INC1000 to change 1,000 feet at a time)
For vertital speed:
To display vertical speed: AUTOPILOT VERTICAL HOLD VAR
To activate / deactivate VS: AP_PANEL_VS_HOLD
To increment: Send AP_VS_VAR_INC
To decrement: Send AP_VS_VAR_DEC