Fair question. I'm not sure he 'switched sides' precisely, looking more analytically than I have done before [having learnt this song at school at age 9, & carried it about as a bit of mental furniture ever since, has rather militated against my analysing all its implications]. Rather, he softened up the listeners by playing 'bonnielie', with the sort of 'spring' which would please the laird, but then

"gae his bags a wheeze
And played anither key"

and launched into some specifically Jacobite repertoire.

Hmmm. Still can't feel 'roguey' that pejorative a designation; feels to me as one might say, "Cor, wasn't he a one!": but must mull over the political implications a bit more.

≈M≈