To reply @Sam2 and @eogks465,
The last place of where you will see
actuator_controls_0 values is usually the attitude controller, hence for Multicopter or Fixed-Wing, you can overwrite (at your own risk) before it publishes to the uORB control outputs topic, usually like the line below
This will be quite an indirect way to change the PWM values since it has to pass through the mixer.
For @Sam2, you can export the ulog file, and the topic would be
actuator_outputs, however this would only be what PX4 send to your rotors, if you are using SITL (you have more control), you can view simulator_mavlink.cpp, from the
Simulator::actuator_controls_from_outputs(), you can change directly what the motors in gazebo will read, since the values will be sent via mavlink under