Brian: interesting cases and I don't know of any exact conventional rules, so IMO it's house rules here on both.
Q1: In Stud, if a player is accidentally skipped when dealing 7th street, how do you correct this? Ex: Player A is dealt 7th face down, Player B is skipped, Player C is dealt 7th and has already brought it into his other down cards before Player B has a chance to correct it.
You can't stop the betting or declare a misdeal, and B has to have a card. Universally, that leaves only the next card in the stub, which would have been C's proper card in order. Likewise C has B's proper card. The law of randomness applies and play must proceed.
The only house option to the above after B is dealt the last card would be to allow B and C to declare all-in prior to the opening bet, but that would be a house rule. I don't hate it. The bottom line is that players join the game with the risk that they may occasionally be dealt cards using the randomness law.
Q2: In a MIXED Game, if a player misses his blind on a button based game and the game switches to Stud, may he re-enter the game during the Stud round?
Please give an example of this... at what point did Player A (the missed blind) join the game? Was he ever dealt a hand in the button round, etc.?