To start, "FM" is what people commonly call "PPM" transmissions to distinguish them from PCM transmissions.

All of the 7C-series transmitters are compatible with your R127Df receiver. The 7CAP and 7CAF come with default airplane programming, the 7CHP and 7CHF come with default heli programming. The arrangement of toggle switches is slightly different to suit the needs of airplane and heli fliers. the "P" and "F" mean that a "PCM" or "FM" receiver comes as part of the package.

Basically, though, whether the transmitter is an "airplane" or "heli" transmitter, or is "PPM" or "PCM", the software is exactly the same in all versions of the 7C transmitter. The default type only dictates what comes up the first time it's powered-up, or the type of model that comes up when you go to a new, unused model memory. Once you've reset them to a different type, that's what will remain.