FIDIC, Yellow Book: Contractor Design related claim

I am managing a Design and build contract Yellow Book FIDIC , whereby contractor has the obligation to design and build the infra works. There is a car park portion having four floors . According to Employer’s requirement the design is different than what he is asked for to design due to the stability of the structure of car park and the structure of future building to be built by others.

The request for changing the design criteria is due to the fact that the car park structure needs to be standalone without having any dependency on the adjacent building structures as beneath the car park there is a metro tunnel is built already and car park is to be built on top of that .

My question is does contractor is entitled to use the BOQ rates for claiming the additional works even though the rates submitted at the time of tender were for design and built and the premium for risk was built in, whereas now for this additional requirement he has the design available for which he has priced the additional cost using the BOQ rates.