From what Marriott says/writes: I can Switch whenever I want - just by telling them befor. And what I learned - for long stays (more than $350 charges) Rewards pay better, for short stays it's Miles (500/stay plus 2'500 per 5 stays).

Problem: my last stay (I want that one with miles) I am not credited yet (it was just 3 days ago), and my next stay is in 5 days (that one I want to be booked als Rewards).

Question: if I switch befor the last stay is credited, do I risk that the old one will be booked as rewards instead of miles? Do you have any practical experience?