If I made any changes prior to building, would it still be acceptable? And if not, where is the line? What is the legal basis, any precedent? How much of the code may I modify before I cross an invisible threshold and somehow "bypass" an "authentication" (neither fit UA anyways, either for law or other purposes unless one can provide any evidence that it ever has).

Bambu clearly didn’t want to press charges on their users, though, so they weaponized the law to try and prevent this, and it’s causing them issues.

In any case, we’re not in some “only the laws matter” reality, we’re also have ethics and morals to consider, in which case Bambu is clearly in the wrong. If they want to secure their servers, they should do it properly rather than using legal threats.