"MacPherson's Fareweel" is also known as "The Freebooter", and was supposedly composed by the man himself, and performed - by himself, no less - immediately before his execution in 1700. The earliest set of the melody I've seen is in the Key of F, tho' I think it tends to be played (on Fiddle, at least) in G or A; and there are many variations, both of melodic line and embellishments. In sowthing over this air, and those I learnt for "R.McC" and "S.S.", there certainly appear to be similarities. Unfortunately for the legend, altho a James MacPherson was hanged in 1700, there's no record of his having been a fiddler. Robert Burns nearly a century later made a song from the Broadside of MacPherson's Last Testament, giving a dramatic and defiant twist to things thoroughly in accord with the potential of the melody.

In a related vein, if "Henry" from all of seven years ago is still around, I found your parallel between the two sets of "Rody McCorley" and the two sets of words called "The Croppy Boy" an appropriate one, though in my estimation the later set, "Good men and true in this house who dwell" (by "Carroll Malone"/Dr James McBurney, late 1830s) is far superior as a dramatic production, whatever may be said of the authenticity of "The Old Croppy Boy", beginning "It was early, early in the Spring" and surely from around 1798. However, to describe Malone's expression of patriotism as "Victorian English" can't be accurate, unless of course the "patriot" to whom you referred is the Yeoman Captain, snarling,
"'Amen', say I, may all Traitors swing!"

The melody chosen by "C.M", incidentally, is "Cailin Oge co Stuire me", the Young Girl from the River Suir, generally attributed to the blind harper T. O'Carolan (see recent thread)