Board Thread:Questions and Answers/@comment-27125665-20151109124016/@comment-25004901-20151109124417

No, you cannot replace a set spell with another one. (Unless a card says to destroy it by effect or whatevs.) Since you can have an infinite amount of set spells, you would just set another one, unless the card says only one of that type (i.e. Green Dragon Knights "Song of Ancient Lands"). As said before, the only way to replace a set spell is if an effect tells you to get rid of it and other things similar to that.