darktable stores noise profiles in an external json file. This file can be found in
$DARKTABLE/share/darktable/noiseprofile.jsonwhere$DARKTABLErepresents the darktable installation directory.
From https://www.darktable.org/usermanual/en/correction_group.html#denoise_profiled
You need to add your json bits there. However, it might be over written the next time DT updates. If you haven’t submitted this to the project for inclusion, you really should.