Yes and no--simply tweaking someone else's arrangement (one which is still identifiably theirs) is still infringement of an arrangement copyright--at least in the U.S. And with most songs, you don't want to change the chords much or you change their intrinsic nature--the performance becomes more of a modern conceit. Copyright laws are now designed to generate undeserved profit for large corporations, so any rationality in their application is not to be expected, particularly in regard to traditional materials.