I just found a wierd article on self-modifying protocols. It is inspired by self-modifying games such as Nomic. Vreeswijk justifies the need for protocols which may be modified in the fly by reference to human conversation, where we constantly modify the protocol in use. For example, I can say "I invented a game called Big Brother", and you will understand when I refer to "Big Brother", I'm referring to a game you may never have heard of before. The article also discusses the bootstrap problem and ensuring that the protocol doesn't go dead. Although there are some interesting ideas, the link between self-modifying games and protocols that are modifiable by the computers that use them seems rather tenuous.

More obviously useful (by which I mean lucrative) would be modifiable-rule computer games. I briefly played BattleTech or some such game, where you can design your mech warrior. The only part of the game that really held my interest was that it felt like I could customize the rules by which the next battle would be played. Of course that's a rather limited sense of rule changing, in that of course the real rules encompass all the possible mech designs. There's also the games where you can design the terrain before beginning the game played on the terrain, like Age of Empires. I can't think of any existing computer game that involves significantly more flexibility than these two types.