Modification

Article 77
The parties may modify the contract upon consensus through consultation. Where provisions of laws and administrative regulations require the modification of a contract to go through approval and registration procedures, such provisions shall govern.
Article 78
A contract shall be assumed as not having been modified if the content of the modification of the contract is not clearly agreed upon by the parties.
Article 2.106 (ex art. 5.106 B) - Written Modification only 84
(1) A clause in a written contract requiring any modification or ending by agreement to be made in writing establishes only a presumption that an agreement to modify or end the contract is not intended to be legally binding unless it is in writing. 85 
(2) A party may by its statements or conduct be precluded from asserting such a clause to the extent that the other party has reasonably relied on them. 86
Article 8.106 (ex art. 3.106) - Notice Fixing Additional Period for Performance 430
Article 8.106 (ex art. 3.106) - Notice Fixing Additional Period for Performance 430
(1) In any case of non-performance the aggrieved party may by notice to the other party allow an additional period of time for performance. 431
(2) During the additional period the aggrieved party may withhold performance of its own reciprocal obligations and may claim damages, but it may not resort to any other remedy. If it receives notice from the other party that the latter will not perform within that period, or if upon expiry of that period due performance has not been made, the aggrieved party may resort to any of the remedies that may be available under Chapter 9. 432
(3) If in a case of delay in performance which is not fundamental the aggrieved party has given a notice fixing an additional period of time of reasonable length, it may terminate the contract at the end of the period of notice. The aggrieved party may in its notice provide that if the other party does not perform within the period fixed by the notice the contract shall terminate automatically. If the period stated is too short, the aggrieved party may terminate, or, as the case may be, the contract shall terminate automatically, only after a reasonable period from the time of the notice. 433
Topic 4 – Alteration
§ 286 Alteration of Writing
(1) If one to whom a duty is owed under a contract alters a writing that is an integrated agreement or that satisfies the Statute of Frauds with respect to that contract, the duty is discharged if the alteration is fraudulent and material.
(2) An alteration is material if it would, if effective, vary any party's legal relations with the maker of the alteration or adversely affect that party's legal relations with a third person. The unauthorized insertion in a blank space in a writing is an alteration.
§ 287 Assent to or Forgiveness of Alteration
(1) If a party, knowing of an alteration that discharges his duty, manifests assent to the altered terms, his manifestation is equivalent to an acceptance of an offer to substitute those terms.
(2) If a party, knowing of an alteration that discharges his duty, asserts a right under the original contract or otherwise manifests a willingness to remain subject to the original contract or to forgive the alteration, the original contract is revived.
Article 450. The Grounds for the Amendment and the Cancellation of the Contract
1. The amendment and the cancellation of the contract shall be possible only by an agreement between the parties, unless otherwise stipulated by the present Code, by the other legal acts or by the contract.
2. Upon the demand of one of the parties, the contract may be amended or cancelled by the court decision only:
1) in case of an essential violation of the contract by the other party;
2) in the other cases, stipulated by the present Code, by the other legal acts or by the contract. As an essential violation shall be recognized such violation of the contract by one of the parties, which entails for the other party the losses, to a considerable extent depriving it of what it could have counted upon when concluding the contract.
3. In case of the unilateral refusal to discharge the contract in full or in part, when such refusal is admitted by the law or by the agreement between the parties, the contract shall be correspondingly regarded as cancelled or as amended.