Using jin to play on chess.com I decided to play a few games on FICS, and I really loved jin's interface. Is there any way to tweak it so that I can connect to chess.com's server? (Or using any other interface, for that matter. In particular, are you absolutely forced to play in-browser at chess.com?)
The chess.com business model depends on locking people into using their site to play through in order to convince those users to purchase subscriptions to the site (just as is the case with Chessbase's Playchess site, the ICC, FIDE Online Arena and several others).  Opening up access to their API (they do have one for their smartphone apps) in the way you suggest could be readily used to break through those commercial barriers.  Which is a round about way of saying, no, there's not much chance of using any other program with their site.