1. Contracts and framework agreements may be modified without a new procurement 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 procurement documents in clear, precise and unequivocal review clauses, which may include price 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 contract or the framework agreement;

(b) for additional works, services or supplies by the original contractor that have become necessary and that were not included in the initial procurement where a change of contractor:

(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 procurement; and

(ii) would cause significant inconvenience or substantial duplication of costs for the contracting authority.

However, any increase in price shall not exceed 50 % of the value of the original contract. Where several successive modifications are made, that limitation shall apply to the value of each modification. Such consecutive modifications shall not be aimed at circumventing this Directive;