Can we run our old personalization and Croct in parallel while we cut over?

we cannot big-bang this. Our old Contentful personalization setup drives a lot of pages and I am not flipping all of them in one deploy with no way back.

What I want is slot by slot: put Croct on a few slots first, leave the rest serving the old way, and expand once each batch is proven. Is that a supported way to migrate, or does Croct expect to own all the slots at once? Rollback story matters to me here.