Charity Seeks Clarity: New Lyrics for Old Songs

Dear Rich: I am seeking clarity about a non-profit educational project that includes a sing-along supplement. I have written new lyrics about money and charitable giving for a number of existing song melodies--most of whose original lyrics do not reference either money or giving. (1) Does this fall into the categories of fair use and/or transformative work? (2) Is simple publication of my new lyrics with "sing to the tune of [name of song]" likely to be problematic? 3) Should I be copyrighting my own new lyrics, either separately or as part of the printed publication? 4) How would you suggest proceeding? Assuming these are not parodies or "rewrites" of the lyrics, you're very unlikely to run into obstacles. Performing, recording the songs, or including the sheet music could be a problem but if you're not doing any of that, and you're simply referencing the songs as a source for the melody, we doubt any music publisher will bother writing a letter of complaint. We also doubt whether a fair use analysis applies because what you're doing is not likely to be an infringement.
Should you register? That's up to you. You get copyright automatically without registration and probably only need it if you're expecting to sue someone.