This is what I did:
(1) I went to Steamapps, took a copy of the AI War directory and pasted it on my desktop. (2) Then I unzipped the version 2.3 patch into this newly created directory, overwriting a lot of files in the proces. (3) Then I launched the game and pushed the update button on the Main Screen. The game automatically downloaded the 2.9 patch and restarted as ZR, trial version.
So now I have two versions: My official unlocked Steam version 2.0 (in a few hours to be 3.0), I can hook up with my friends and expect to play without problems, everything is playtested and official. And I have a locked version 2.9, soon to be 3.0, then 3.01 etc., where I can try out all the new gear as it gets invented. (Locked for now, as soon as I can get my hands on a VISA card I intend to unlock it). This will be my working or experimental version of the game, where I can test all the new toys and rule changes.
For serious multiplayer campaigning I still have my official version, that sticks to certain rules of a certain date/version.
This configuration seems so far to work allright on my computer. I haven't tried multiplayer yet, though. I hope I am not causing the game to crash on me or something by these actions? I am not totally computer illiterate, but I sure have a lot of self-inflicted ctd's on my conscience.
Btw, AI War has never made a ctd on me so far. +10 rep