The park can request whatever they want. Plain and simple.
I think people don't realize how much the park influences the coaster. Coaster companies only offer ideas and possibilities. The parks are the ones who request specifics, such as layout, track type, trains, location. The park creates the ideas, the company makes it happen. The park is the architect and the company is the engineer. If the park wants something proven for 20 years, why not? If the park wants something new and different, why not? I wouldn't say this was a decision by B&M at all, but a decision by KI.
I would say you have absolutely no idea whose decision it was. You would guess KI, I would guess B&M. KI could've simply said they'd like to see the design "updated" and B&M sold them on the idea of the new restraints.
Don Helbig said in an interview that B and M was the one that pushed the new restraints not Kings Island.