It looks like everything else is preliminary to the hypothetical ballot and not in itself meaningful to you, but I’d still have to make a few points. (1) Trump was registered as a Democrat specifically in NY. Despite some affinity between his right wing populism and the populism that exists in a branch of the Democrats, I’d presume this had a lot to do with the local environment in a very blue state. Lots of people here are very much Republicans but are registered as Democrats because a lot of races happen for real in the Dem primary. Pittsburgh has (or at least had) the same situation. And it’s part of the reason we have problems with the Independent Democratic Conference. (2) The Democrats and Republicans have different rules for primaries. It’s not a given that what Trump did to win the Republican primary is possible in the Democratic Party. It’s especially hard for me to imagine Trump winning there where Sanders couldn’t. (3) People like to pretend it doesn’t matter, that each candidate is purely an individual, but political networks are absolutely important in our system. If Trump were a Democratic President, he’s just not going to be appointing the same people to various courts or administrative positions. It’s not really possible to say he’d be the same person. You’re hypothetical seems to want me to assume otherwise, though, so I will.
I preferred Cruz in the primary, because while I think he’d shrink our democracy I felt Trump would break it. I feel the same way now. If Trump were running as a Democrat but truly arguing the same things and allied with the same people, I’d think I’d feel the same way.