WE are operating an NEC3 ECC option C contract and we had agreed the Contractors share ranges at the tender stage. However, in hindsight we believe that the ranges are on the small side and we believe it may not be incentivising the Contractor in the way we had hoped for.
Can these be renegotiated with the contractor by using clause 12.3?
Providing both Parties agree then yes this can be done. I doubt the Contractor will stop you from changing them if they will be for their benefit.
There is no reason why the terms of a contract cannot be changed by agreement between the parties, subject to clause 12.3 which requires any changes to be in writing and signed by the parties.
So to answer your question, yes it can be renegotiated, but any subsequent agreement must be in writing and signed.