The OECD has issued rules on the profit attribution between headquarters and permanent establishments known as Authorized OECD Approach (AOA). This regulation proposes that permanent establishments should largely be treated likewise separate entities.
Yes, basically the application of the AOA is mandatory from 2013 onwards. Existing cases can be finished under old rules. From 1 January 2015 onwards Germany implements a detailed regulation that provides concrete guidance on the application of the AOA.
In principle not. German law stipulates application of the AOA together with a treaty override. However, if a different treatment under the Double Tax Treaty (DTT) is possible or required and the other country applies the rules accordingly, a different treatment is possible.