Hey Steve,
There are others on this list that know more about this than I do, but I'll take a shot at giving you an answer.
The vertical stabilizer already is mounted off center per the plans! About 1/4" at the front if I remember correctly. This is the amount Vans has determined to be "about" right.
It will need to be different at every power setting, so trying to adjust it by moving the stabilizer would be a real pain.
I'm not flying yet but I think most folks just glue on a small trim tab after making test flights to determine what they want.
I have seen at least one person who had devised a spring biased rudder trim that could be adjusted inflight easily.
Hope this helps ,
Mark