"I don't enjoy the B music of The Quaker being grafted onto the A music of Walter Bulwer's No. 2 polka "
Someone complained about this elsewhere a while ago, and I discovered the most likely culprit - it's printed like that in Nick Barber's "English Choice" book (pub. Mallinson). He's quite unrepentant and also a good friend; I'm not about to pick a fight about it. I know several people who have learned it that way though.

I am personally responsible for several people learning a Playford tune called "Jack's Health" wrong (bar missing from the A music) because I learnt and then recorded it that way. Also we don't do The Dennington Bell the way most Suffolk musicians do (including Dolly Curtis who was the source of the tune), because we make it into a regular 32 bars.

And I recorded "The Dunmow Galumph" as written by Doug Adams, but not the way most bands and musicians have played it ever since.

I don't count a key change as a substantial modification to a tune - you transpose it to whatever fits the limitations of your instrument if it's one of many folk instruments that only works in certain keys (melodeon, anglo concertina, pipes, whistles). But I've been having fun recently trying out lots of tunes on C 1-row melodeon, and it's amazing how different some of them sound and how quickly you are tempted to make modifications to suit the sound or range of the instrument.

Anahata