How can I alter apt-add-repository to support other Debian-based distributions?

I'm using a Debian-based OS distribution (Devuan, to be specific). I'm trying to use the apt-add-repository Python-based program, which is part of the software-properties-common package . Unfortunately, running it - fails, and I get:

Traceback (most recent call last):
  File "/usr/bin/apt-add-repository", line 361, in 
    addaptrepo = AddAptRepository()
  File "/usr/bin/apt-add-repository", line 39, in __init__
    self.distro.get_sources(self.sourceslist)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/aptsources/distro.py", line 92, in get_sources
    raise NoDistroTemplateException(
    ......
    )
aptsources.distro.NoDistroTemplateException: Error: could not find a distribution template for devuan/excalibur ceres

I've gone over the script itself - the "templates" are not there; I've also looked through a couple of potential files it imports, also no luck, or perhaps I've missed something. My questions: * Where are those "distribution templates" actually located? * How can I add a template to suit my distribution?