Sorry, mis-read your question...
You can shorten the a-arms, but that will increase the camber gain, shorten the instant centers and change the roll center of the front end. In short, it will alter the way the front end reacts over bumps and while cornering. It will likely make the car have more body roll which a anti-roll bar (sway bar) will help counteract. You will of course have to also shorten the tie rods a similar amount so you can set the toe. If you are not going racing, you will likely be okay, and if you end up not liking it you can always re-install stock a-arms and change your wheels to make everything clear.