If the Contractor is obliged to perform work (Werkleistung) or to supply labour and materials (Werklieferung), BMW can at any time up until acceptance demand changes and additions to the order as it sees fit and having due regard for the interests of the Contractor. The Contractor is under a duty to suggest changes to BMW, which it considers necessary or expedient with a view to successful performance of the contract. It shall also execute said changes following written consent by BMW.