RB drivers are all signed to RB, not RBR/SAT. That’s why they can swap them around mid season so easy. The drivers don’t drive for either team technically, they drive for the parent company.
I'm really excited for Yuki's future as this season he really has done an exceptional job with the equipment provided. If Yuki continues to impress/beats Daniel handily in the same machine I'll be a sad he isn't getting a go at a top team.