Steve, there is a way to choose the cpu line up, using Shailesh's gaMCHange tool. You need two controllers or a controller and a keyboard though, and it's a bit of a fiddle but works, and will do for the time being until a line up editor is released.
1. Start the match as 2 player, team 1 as keyboard and team 2 as controller (or controller 1 and 2 if you've two controllers).
2. Choose both the line ups.
3. Start the game, bowl 1 over using both controllers (a bit tricky, but possible; I've done it before in c2k4. Just bowl outside off and leave the ball).
4. At the end of the over, save and quit the game.
5. Go to Gamchange, swapping say, team one (or whatever one you don't want to play as) to cpu controlled.
6. Restart and away you go.
As I say, it's not ideal, but will do until a line up editor is available

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