By Value Engineering I assume you mean a change promoted by the Contractor for the Employer to reconsider his requirements/Service Information to enable a cost saving.
Under Option C, clause 63.11 provides that a compensation event which reduces the Defined Cost will not result in a reduction of the Prices if it is a result of a change which the Contractor proposed and the Service Manager accepted.
Therefore a proposal to change the Service Information (VE) made by the Contractor would not change the Prices and both parties would share the saving under gain share.