Wow! Bruce, you're as avid a researcher as I am. I'm nost surprised that "blackbird" would retrieve so many different listings. That particular species figures in MANY different ballads and songs. I agree that the reference to Bonnie Prince Charlie in the one example is false. Don't think, from what I've read, that he was ever referred to in that way. Bonnie Dundee could possibly have been called blackbird at one time or another...portraits show him dressed in black armour, with long black hair.
Blackbird certainly fits Parnell though. He seems to have been quite striking, with piercing eyes, and a black beard. He was of the Irish ascendency and I think it must have surprised some people that he became such an avid promotor of Home Rule. His home in Avondale is now part of the Forestry School in Ireland, and it's a grand place to take a tour. The setting is gorgeous!
As for the tune making it's way to Ireland, it probably came with some of the Irish who were supporters of the Jacobites. Irish republicans would have supported (and did) anyone who was fighting against the English.