Allan--

I'm sure that's a good site & I plan to check it myself. In the meantime, for a quickie answer: You can generally go up a whole step on the last verse to 'pump up' the ending. For more ambition, I've heard "Sit Down Young Stranger" (Lightfoot), which is a conversation, taken up a whole step every time the speaker changes. That takes vocal range. Also heard 'progressive' Amazing Grace taken up a whole step on every verse. That's for multiple voices so the harmonies change as it goes up and different parts become possible-impossible.

Another simple thing that works is ending a minor song on the parallel major. (The fancy way to say 'the major on the same note as the minor,' so you don't have to bother with relatives.) Like, I do "Wayfaring Stranger" in Am, but on the last note, play A. Or having done a few verses of "House of the Rising Sun" in the blues version in Dm, change to Woodie's version in D.

Only thing I know about passing chords is that you can go from G to C via G7. I'll pick a melody in G and then just pass G-G7-C, which means the highest note on the high E is moving down, but then you fool 'em because when the melody starts again in the key of C it's higher than it was in G, not lower as the downward progression might lead one to suspect.

For whatever that's worth.

CC