This is in case there's any male Lynn who's had a Y-DNA test and did not match other Lynns but did match Blairs. I've been tracking one particular Lynn family in the Scottish census and found the following, which suggests that a boy whose father was a Blair had his name changed to his mother's maiden name - Lynn.
1861 Census of Scotland - E.D. 1, Larbert, Stirlingshire William Brisbane, age 18, Head, b. St Ninians, Stirlingshire, Ploughman Agnes Brisbane, age 22, Wife, b. IRE John B. Blair, age 2, Stepson, b. Larbert
1871 Census of Scotland - E.D. 1, Larbert, Stirlingshire William Brisbane, age 28, Head, b. St Ninians, Stirlingshire, Railway Labourer Agnes Brisbane, 31, Wife, b. Ballymena, Antrim, IRE John B. Lynn, 12, Son, b. Larbert, Iron Moulder?? And younger children listed as Brisbanes.