Send custom message from MAVProxy to RC Remote (PC -> MAVlink -> FC -> SPort/FrSky -> RC transceiver -> RC Remote)

Hi everybody,
Currently, I’m using the “FrSky SPort Passthrough” option (SERIALx_PROTOCOL = 10) to send telemetry data from the Pixhawk CubeOrange flight controller (FC) to the RC remote. The RC remote is running OpenTX and the Yaapuu telemetry script. This is working fine as intended. When I discover sensors on the RC remote, the default sensors (VFAS, CURR, ARM, etc.) appear.
Now, I’ld also like to send custom status information from a companion computer (PC) to the RC remote using MAVlink. My preferred method would be to send a corresponding packet/command from the PC to the FC via MAVlink. The FC should then forward the data to the RC remote via SPort/FrSky telemetry.
Hence, the question: Is it possible to enable an additional sensor on the FC where I can write simple integer or float values to? Is it possible to set the data of this additional sensor via MAVlink commands?
Or is there maybe an easier way to send data directly from the PC to the RC remote?
(Btw: I was already able to make some minor changes to the firmware source code and compile it successfully.)
Many thanks

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