I would imagine that if it were possible, it would have more functionality than merely changing region/language. Not just looking at 'cheats', either. Some of the stuff you can do with the Neo UniBios is pretty darned cool.
From a technical standpoint it'd be interesting to have something like this available. Though I just don't see the demand being big enough especially with region options being there by default.
Region changes are basically there by default on a huge percentage of neo geo carts (English/Japanese). Like I said I'd just like to be able to pause a game mid play or some other useful features.