I think everyone is free to release and sign players at all times, even though there's still one pick to be made.
I'll alter my bench somewhat and release some dinosaurs:
- Yaya Toure
- Wayne Rooney
- Fabio Coentrao
Instead, I'll sign:
- João Mário (INT)
- Jeison Murillo (INT)
- Lucas Moura (PSG)
No, this is not allowed, especially when there is still a pick to be made.