Copyright question

Hi all, I'm very very new to the whole MP3 tagging process, so please forgive the bad question.

My question is, if I want to write a software that automatically edit or modify the variables of multiple tags of MP3 files, do I have to worry about any copyright or patent issues?

That is (1); on the music file itself, will I be violating any copyright rules for modifying the tag of the purchased MP3 files.

AND (2) for the ID3 tagging method itself, are the fields freely available for editing or what do I need to do in order to modify them? - Say, I see there is a bunch of new fields for ID3v2.4 that didn't exist for ID3v2.3, can I freely assign values to them without running into troubles?

Thank you so much for your comments, and I'm sorry if this seem to be a silly question.