(1) Where the customer seeks to obtain
1. a modification of the agreed result to be obtained by the work (section 631 (2)) or
2. a modification necessary to achieve the agreed result to be obtained by the work,
the contractual parties will strive to reach mutual agreement regarding the modification and the augmented or reduced remuneration to be paid, as a consequence of the modification. The contractor is under obligation to prepare an offer for the augmented or reduced remuneration; however, this is the case in the event of a modification pursuant to sentence 1 no. 1 only if the execution of the modification reasonably can be expected of the contractor. Where the contractor asserts internal processes within their operations as the reason for which the contractor cannot reasonably be required to comply with the order pursuant to subsection (1) sentence 1 no. 1, the burden of proof will be incumbent on the contractor. Where the customer is responsible for planning the building or the outdoor facility, the contractor is obliged to prepare an offer for the augmented or reduced remuneration only if the customer has prepared the planning necessary for the modification and has made it available to the contractor. Where the customer is seeking to obtain a modification regarding which the contractor is not entitled to a claim to remuneration of increased expense and effort pursuant to section 650c (1) sentence 2, the parties will strive to reach mutual agreement solely regarding the modification; in such event, sentence 2 does not apply.
(2) If the parties fail to reach mutual agreement in accordance with subsection (1) within 30 days of the contractor having received the request for modification, the customer may order the modification in text form. The contractor is under obligation to comply with the order issued by the customer; however, the contractor is obliged to comply with an order under subsection (1) sentence 1 no. 1 only if the execution of said order reasonably can be required of them. Subsection (1) sentence 3 applies accordingly.