I'm sorry, but you don't know what a "yellow dog Democrat" is. See my post 14.
And no one has even attempted to answer the question: if they can't be Republicans, why don't they at least start their own party? Why is great-great-grandpappy's honor not besmirched by Nancy Pelosi the way it is by Lincoln's party?
The rules basically force a 2-party system. In order to get committee assignments they have to vote for one candidate for Speaker or the other. Thus Bernie Sanders, Joe Lieberman, et al. are Democrats, even if they didn’t run under that label.
My opinion on that question is that, if they were concerned and interested enough in politics, and if they were clear-eyed enough to really see what is going on, then great-great grandpappy's honor would be the least of their concerns. They wouldn't be forming a new party, they'd be conservative and primarily voting Republican. They'd be part of, or at least sympathetic toward, the Tea Party.
Again, that's my opinion. I'm as Southern as you can get. My family has lived in the South since before the Revolutionary War. I had family members who wore Confederate gray. My parents probably voted Democrat most of their lives.
I've voted primarily Republican since I was first eligible to vote; my first vote in a Presidential race was cast for Ronald Reagan. I don't care which party was on what side in 1865. I care about what is happening now, and six months from now, and two years from now, and five and ten years from now.
I think about politics and policy and such things. I don't believe most Yellow Dogs do think about those things, much. They think about what's going on in their own little world and how the Braves and the Falcons and the Dawgs or the Gators or the Tide are doing. They remember what Daddy or Grandaddy or Uncle Bud or whoever told them about politics and politicians. They remember the local sheriff back when they were a teenager and how he was known by half the county as "Uncle" and how he helped them get out of a ticket or get home when they were "just a little tipsy" or how he helped a family member get a license without all that botheration- and he had a big "D" after his name on that ballot. Politically, they live in the past.
Why don't Blue Dog Democrats form their own party? Because, if they did, they would lose the votes of the Yellow Dogs.