I see you didn't grow up cracking apps and games, this is quite easy with a hex editor and bintools. Well, until codesigning came along, but that doesn't seem relevant to this analogy.
Cracking a binary circumvents authorization to provide full access to functionality the program already has. That’s very different from modifying the program to add new features.
Only distribution.
But even if distribution is required to trigger the law - you are free to distribute fine-tunes of most open weight models.
Depending where you are it might be "DRM circumvention" all the way up to some bollocks hacking charge.
It's pretty murky in places because lots of copyright laws protect DRM but also have carve-outs for personal backups.