I'm sure I'm not the first one asking this.

Is it allowed in a Limited GP to drop before deck swapping?
In the TR I find that you will get a match loss in the first round if you drop before deck swapping.

I have the feeling it can be considered theft of tournament material, but I can't find it there.

http://apps.magicjudges.org/forum/topic/4477/ is slightly relevant.

In practice, I believe most, if not all, GPs allow this practice.

Technically it isn't allowed.

Please continue this - if further discussion is needed - in the thread linked by Dominik.

Thanks!