Aren’t all the new achievements multiplayer specific? If so, then I think what you want to do might be considered boosting.
i don’t know. I’m kind of murky on the whole “create a party to work on achievements” thing since the other day me and some people from this forum got together to do the Bros to the Close achievement.
Any official clarification would be handy.
Edit: Yeah, just double-checked. They are all matchmaking achievements, and although I don’t think they offer any more benefit than increased gamerscore, you probably want to not go about getting them like you are wanting to.