Article 29 addresses modification (which includes an
addition to)1
and termination of an already concluded contract
by agreement of the parties. According to article 29
(1), the mere consent of the parties is sufficient to effect
such a modification or termination. If, however, the parties
have agreed in writing that a modification or termination of
their contract must be done in writing, paragraph 2 provides
that the contract cannot be otherwise modified or terminated—although
a party’s conduct may preclude it from
asserting such a provision to the extent that the other party
has relied on that conduct.