You can add a lot of relative minors to 3-chord trick songs to tart them up a bit. But whether you will thereby improve them is a matter of personal taste. As a test, obtain listen to Bob Dylan's original recording of Blowing in the Wind, and compare it with the Peter , Paul and Mary cover. To my ears, the cover sounds mawkish and emasculated because of the extra chords. Others think the reverse. Try it and see: get it right for you.