How will FHR benefit works with a separate stay booked immediate before the FHR booking


So I am planning to stay 6 nights at one of the 4 seasons.
I found first 5 nights with great rate for the room 2 - 3 level above base room without Breakfast
The FHR benefit for this specific 4 seasons offers 100 SPA credit + Room Upgrade+Breakfast and guaranteed 4PM checkout.
If i book a base room on the 6th night using FHR and asking at check-in to combine both reservations, will I still get SPA credit , late checkout and breakfast on the 6th day?
Since I will be booking only the base room, is it likely they will just combine the 2 reservation and upgrade us to the same room on the 6th night?
We are going to do at least 1 SPA service anyway, so the $100 credits is kinda like full value to us.

Anyone did something like this before?

So my plan is to stay 5 nights at four season using a prepaid booking which offers great value. I will