This isn't really relevant to the legal status of a change (i.e. patch) to a proprietary work where the source code is public. The answer is that making the ch

This isn't really relevant to the legal status of a change (i.e. patch) to a proprietary work where the source code is public. The answer is that making the change is already usually copyright infringement (though I think some countries have a concept of private copies being exempt from these types of restrictions). But redistribution of your patch would definitely be copyright infringement because a license to create a derived work was not given to you -- and patches are by definition derived works.