Lighter, I'm not sure, but I think the clue is that "he did not understand the unique characteristics of Irish music, such as modes".

I'm a self taught musician so I'm not claiming any in depth knowledge, but here is my guess.

So if he looked at a tune and for example, the first (not counting any lead-in notes) and last notes were C, then he could possibly assume that the tune was in the key of C Major, and then he would fiddle with the accidentals to make it fit that key. If it was in fact a modal tune, then - I think - the key should be identified by the sharps or flats in the tune and not the start and end notes.

That's about the limit of my knowledge apart from the fact that there are different modes depending on where the tune starts and ends and each mode has a specific name and sometimes a type of "feeling" attached to it, e.g. the minor key i.e. Aeolian mode has a more haunting or melancholy feeling than the major key.

My question about Give Me Your Hand is the accidental in the seventh last bar where in the key of G Major, the high F sharp note is played as an F natural. On a harp without levers, which I assume an old Irish harp would be, then that accidental note would be a curve ball however, since there is no other high F sharp in the tune, that string could be tuned down a semi-tone prior to playing the tune.

I noticed in the video on the Wemyss page that I linked to on 11 Oct 19 - 08:22 PM that the harp player did not play that accidental.

Given that the Wemyss manuscript was lute transcriptions it makes no sense to change a sharp note to a natural because a lute player could play the correct note easily, however if the lute players learned the tune from harp players other than Ruaidri Dáll Ó Catháin then maybe they didn't play the accidental either. Maybe it was a bit of a marketing trick by Rory Dhall to differentiate himself and his ability from the competition. (Sorry. Can't help looking at it from the angle of what I learned at Uni about management and marketing. LOL)