From my understanding of laws in Germany, in Germany, you're allowed to do all of this if your goal is interoperability of systems.

If your goal is to not pay them money - which you strategically unwisely hinted at with this question - then that's not covered by that exemption, I think.

So from my understanding, adding new music and releasing the tooling for that should be fine, but IANAL.

Frankly, what is or isn't legal doesn't matter as much as your story, as you will be judged by that. It also helps if the story is actually genuine, but that is a somewhat optional requirement all things considered. At least the industry treats it as such.

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FWIW, as these capabilities trickle down to everyone through LLMs, it is worth asking yourself whether it is worth the trouble of releasing it in the first place.

If anyone can replicate this within a reasonably short timespan, then maybe not.

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With this stuff in particular, it's also worth considering the business model of the entity.

Does your work pose a relevant risk for their bottom line? If yes, then bad. If no, then shrug.

Is music sold their main revenue channel, or are they just also doing that because recurring revenue is nice to have?

How user-friendly would you want your work to end up as? Would it target the demographic that would otherwise just buy the music?

Truth is that this is all just an elaborate dance.

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To close the "polish trains" gap in what I just wrote in the last section:

"Is their business model ethical? And is it considered that by the majority, common sense, and politicians?"