It seems fairly common to re-purpose tunes with new lyrics. “Tramp! Tramp! Tramp!” becomes “Jesus Loves the Little Children”, “John Brown’s Body” becomes “The Battle Hymn of the Republic”, etc.
It seems less common that lyrics are set to new music. Is this true, or have I just missed a bunch of examples?
The thing that got me thinking about this is the example of both below.
Happens all the time. Look at Schiller’s poem “Ode to Joy”. Every one knows that Beethoven wrote music for it.
Other people who wrote (other) music for the same poem are
C.G. Körner
C.F. Zelter
J.F. Reichardt
L-W. T. de Ferguson
J.F.H von Dalberg
J.R. Rumsteeg
F. Schubert (you may have heard of him)
P.I. Tchaikovsky (or him)
P. Mascagni
J. Strauss II
Z.R. Stroope and
V. Poleva.
My favourite retuning of the words is the Carol “While Shepherds Watched their Flocks by Night” to the tune of “Ilkley Moor”.
Sounds excellent.
Years ago a Folk Club I went to had a regular annual night where contributors were invited to sing a song to the tune of another one - and to challenge others to sing a song to a particular different tune. I remember singing “Pop goes the weasel” to the tune of “God Save the Queen”. Or was it the other way around?
It’s also a feature on “I’m Sorry I haven’t a Clue” (BBC Radio 4). http://www.youtube.com/watch?v=qYGMvH2FBR4
Sure, why not?
“The Lily of the West” by The Chieftains and Mark Knopfler: http://www.youtube.com/watch?v=2KAzzFE_8OE
“The Lily of the West” by Tabache: https://itunes.apple.com/us/album/are-you-willing/id263100359
Not quite a different tune, but a very different arrangement:
“The Maid of Coolmore” by The Bothy Band: http://www.youtube.com/watch?v=ySnJyHjbca4
“The Maids of Culmore” by Paddy Keenan and Tommy O’Sullivan: https://itunes.apple.com/gb/album/the-long-grazing-acre/id41526864
The words are different enough that it’s probably not the same song:
“The Raggle-Taggle Gypsy” by Planxty: http://www.youtube.com/watch?v=JyP407UnUWw
“The Gypsy Laddie” by The Tannahill Weavers: https://myspace.com/tannahillweavers/music/song/the-gypsy-laddie-39379696-41724788
With Christmas carols it seems to happen more often.
“It Came Upon a Midnight Clear”: http://www.youtube.com/watch?v=Ghpv7_iKeJU vs. http://www.youtube.com/watch?v=KtV477Cqni0
Same thing with “Away in a Manger”, “I Heard the Bells on Christmas Day”, et cetera.
Crossing with others, but …
Yes, you have. 
In fact, your choice of “Amazing Grace” is a good example, because hymnody is a genre where that happens all the time. Look up a particular hymn by the words, and you’ll find a number of different melodies that it has been set to.
Similarly with sacred music, where many composers have set a well-known biblical or liturgical text to their own music. The several popular versions of “Ave Maria” may be the best known example of that.
Or ballad tradition. Pick any text from the Child Ballads collection, then seek out performances of it. You’ll often find a surprising variety of different melodies used.
Ethnomusicologically, in the case of ballads the role of print technology is interesting. Originally and in the wild, ballad instances are, of course, bundles of words and music, not disembodied tunes and texts. But broadside balladry led to a focus on text, partly because of the cost and difficulty of typesetting music. Then later post-Romantic collectors and enthusiasts, including many of Child’s print sources, were literary-oriented and tended to collect and value disembodied text as poetry over tune. In that climate, it’s doubtful for example that Coleridge had vocal tradition or melody in mind in writing The Rime of the Ancient Mariner (though others tried to remedy that ex post facto, with ahem questionable results). It’s really not until Sharp and Karpeles and their heirs, and the advent of sound recording, that mainstream literary culture began redressing the balance. But even today, well-known ballad settings are often a modern result of a folk performer choosing a text and composing or selecting a melody to go with it. Not that that melding wasn’t sometimes part of the original folk process itself. Things come full circle …
You weren’t thinking of this, were you? It’s a classic!
No, but that’s fun. Thanks!
Let’s see, what rhymes with “noon”? Oh no - the worst rhyming cliché in the book: moon, June, croon … I need something different …
And ate a macaroon
And spat in a spittoon
And barked like a baboon
For something something bassoon …
That’s it! Did they even play bassoons back then? Aw, who cares. Bill W. and his insufferable sister will be here any minute and he’ll expect a reading …
Balloon, maroon, vinegaroon, swoon, impugn…oh, hell. Here’s a list:
http://www.rhymer.com/RhymingDictionary/balloon.html
They missed “attune”, for one.
Interesting, I guess I am more likely to find tunes and find the lyrics that have been set to it than the other way around, hence not being to think of any examples off the top of my head.
Always meant to set Burns’ O Wert Thou in the Cauld Blast for men’s choir/quartet to the tune of O Waly Waly… just never have gotten around to it yet (but the idea came about in large part because I didn’t know there was already an associated tune).
Except for the middle 16 bars and end, Grand Funk Railroad’s
I’m Your Captain goes perfectly to Will the Circle Be Unbroken.