I think you could do this by changing the value function”

The essential thing with AlphaZero is that it doesn’t have a value function that you can change. It learns it from the games it plays against itself.

The best you could do is train it by playing against some algorithm that plays aggressive romantic style (playing against humans playing aggressive romantic style would work, too, but that would make for slow training)

I doubt that would produce an AlphaZero that itself plays aggressive romantic style, though.

Edit: one thing that _might_ work is to, during training, change the rules of chess to “both players lose if the game lasts over N moves” for some small N (40?). That should put incentives on aggressive play. Disadvantage would be that AlphaZero would learn very little about endgames.