When I was on an admission committee it always disbanded after the acceptance letters were sent out. Anything that happened later - admitting people off the wait list, adjusting financial aid, talking to disgruntled rejected students - was all handled by administrative staff, occasionally escalated to an associate dean. There was a little flexibility in financial aid built into the budget, for those where "additional circumstances come to light." That's where you can do a little bargaining - but you have to approach it like you're telling them something new about your situation. It won't usually be admissions committee members involved - they won't even know about it - so how much they want you is just boiled down to a ranking or tier in your file, and the admin staff may be authorized to negotiate with 4's, for example, but not with 3's or lower. This is why some people have better success in trying than others. It doesn't usually hurt to try - though in my university the drama school has been known to pull offers of those who repeatedly ask (but of course they're more dramatic than architecture administration).