The contractor is only required to submit particulars of its design for acceptance as the works information requires, see clause 21.2. Therefore, if the works information does not require any such submissions, then the contractor is not correct in suggesting that the design should be submitted for acceptance.
There is no need at all for the submission of design for acceptance. You should therefore return any such design and explain that acceptance of it is not required under the contract. This also means that you do not need to add the suggested insertion into the works information.
It is important to understand that, in any event, acceptance by the project manager of the contractor’s design does not change its liability for that design, see clause 14.1.