Yey but in my special case i'd like to involve the changes in a sysprep-operation atuomatically.
I solved this issue by a <SynchronousCommand>-order in the answer file so that a batch-file starts at the end of the sysprep-process.
And this batch-file itself starts a reg-file in silent mode which makes the changes in the registry. ^^
So mutch work for such a little change - but thats the only way it works automatically i think :-/