Suppose I submit a copy of my 9 songs to the copyright office. Then, after it has been submitted, i alter a few of the levels of the instruments in the tracks and re-eq'ed here and there. I have not added any new instruments, added or taken away any melody/harmony, or rearranged the song order. Does the copyright still hold 100%? Would it be smart to resubmit a new version? Or is it not necessary in this case?