I could be wrong, but I think the only thing that is limited to just first years is the MacPass. Even without the MacPass, you can still get into most of the events. I think the jumpsuits you're referring to are the Welcome Week Reps. Those are upper year students who organize Welcome Week.
I would think transfer students count as first years, since it's your first year at Mac. You can email the First Year Experience Office and ask:
[email protected]