During the course of the arbitral proceedings, a party may not amend or supplement its claim or defence, including a coun- terclaim or a claim for the purpose of a set-off, unless the arbitral tribunal considers it appropriate to allow such amend- ment or supplement having regard to when it is requested or prejudice to other parties or any other circumstances. However, a claim or defence, including a counterclaim or a claim for the purpose of a set-off, may not be amended or supplemented in such a manner that the amended or supplemented claim or defence falls outside the jurisdiction of the arbitral tribunal.