X-Aviation G5 with X-Plane C-172 not working with Autopilot modes

[ScottR]

Hello. I have recently purchased the X-Aviation RSG G5, which comes pre-installed in the X-Plane basic C-172. I am attempting to improve the Air Manager GFC 500 functions, so that they are more realistic to the actual autopilot. As I have dug into the datarefs for the X-Aviation C-172, I've found that the sim/aircraft/autopilot/ah_source is set to 13, which according to the documentation is "turn coordinator and absolute pressure transducer". The sim/aircraft/autopilot/dg_source is set to 10, which is "AHRS".

Both of these datarefs are marked as not editable.

Since the ah_source is not set to "AHRS", the autopilot cannot control the pitch angle, as the GFC 500 does. Does anyone know how I might reset the ah_source value to 10 = AHRS?