You can indeed do this, however it is best to have a notar countersign it for you or have an American will written up to be applicable globally.

Actually the pflichtteil is a bit worse than it sounds unless you have children when you can act as your childrens guardian and decide on their behalf ie you keep the money. The pflichtteil can be at the insistence of the relative immediately payable which might, and I know cases where this has been the case, mean selling the house and there is B****er all you can do about it... And it actually drops down and back up the family tree ie if your parents are dead your brother or sister can land the money... Very similar system to Germany...