1. Concessions may be modified without a new concession award procedure in accordance with this Directive in any of the following cases:
(a) where the modifications, irrespective of their monetary value, have been provided for in the initial concession documents in clear, precise and unequivocal review clauses, which may include value revision clauses, or options. Such clauses shall state the scope and nature of possible modifications or options as well as the conditions under which they may be used. They shall not provide for modifications or options that would alter the overall nature of the concession;
(b) for additional works or services by the original concessionaire that have become necessary and that were not included in the initial concession where a change of concessionaire:
(i) cannot be made for economic or technical reasons such as requirements of interchangeability or interoperability with existing equipment, services or installations procured under the initial concession;
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