Article 21Amendments
The contracting authority and the contractors may change the contract by an amendment on condition that this amendment fulfills all of the following conditions:
(a)
it does not alter the subject-matter of the contract;
(b)
it does not disturb the economic balance of the contract;
(c)
it does not introduce conditions which, if they had appeared initially in the contract documents, would have allowed for the admission of tenderers other than those initially admitted or would have allowed for the acceptance of a tender other than the one initially accepted.