Would something like that work for you? It gets installed with the UID from the YAML. Since that is just a string, one could also edit it to use a more "useful" name. The added transformation is not editable.

https://community.openhab.org/t/testtopic/156092

I think it's probably OK that the transform is not editable. Transforms are usually going to be short compared to a rule template so if it doesn't do what one wants, they can copy/paste/edit themselves.

The YAML looks good. Nice and simple.

When you say "edit it to use a more useful name" do you mean the author of the transformation can change that or that the end user can change it? Either is reasonable in my book, I just want clarification.

All transformation types are supported or only some? I really only expect to see Script transformations published but who knows what people will come up with. Maybe there's a hidden demand for Map transformations. So the type filed is the language of the transformation for sure based on that example, but if it's not a Script would I use "map"?

Thanks a bunch for working on this! I'm really looking forward to having this new feature!

That works for every transformation type, a MAP would look like this:

uid: config:map:aGermanMapForOpenClosedType
label: maptest
type: map
configuration:
  function: |-
    CLOSED=zu
    OPEN=offen
    NULL=undefiniert

Regarding the name: This uid is used excatly like it is in the YAML (or JSON, you can also use JSON). So the "developer" of the transformation can set it.