GWSignal source model incompatible with adding new waveforms
From this line, it looks like bilby will only let a user use GWSignal interface if calling SEOBNRv5PHM, SEOBNRv5HM, or IMRPhenomXPHM (in which case it will log a warning). If the waveform is not these, it will raise an error. Even though new or custom versions of GWSignal may be able to call different waveforms, bilby will not let it.
GWSignal already includes a check if the requested waveform is implemented. I think bilby should not raise an error here and let GWSignal raise the error if the waveform is not implemented. Or else, gwsignal_binary_black_hole
in source.py will have to be updated every time a new waveform is added to GWSignal.