Booking with an inside with CN and upgrading later?

[CookieShip]

Since there is the double up offer this month, I was thinking of booking a sailaway inside room with 2 CN before the end of the month.

I'm hoping the sailaway balconies will drop a bit more, when it hits my sweet spot, could I upgrade to the balcony then? Paying the difference, which will hopefully be small. 

 

If it doesn't happen or the balconies somehow become all sold out, we could live with an inside.