By all means make whatever changes to a traditional song that you feel are appropriate; provided that you tell your audience what changes you have made, and why. There is a big difference between the normal, usually gradual, changes that occur in the course of oral transmission, and deliberate changes that may alter fundamentally the tone or meaning of the song. We owe some respect to the material that others have given us, and that means that, while we are free to interpret that material in any way we see fit, we also have a duty to make it clear where we have made changes to it. The fact that this has not been the normal practice in the past is beside the point; times have changed. Of course, a song that seems to require substantive alteration before you are comfortable singing it may simply be the wrong song for you in the first place.

Malcolm