I'm uneasy about you actually being able to use your tickets on the 10th, as well.
Maybe there will be no problems (I hope so,) but I am loath to just take the assurances of just one CM on the phone.
EDIT:
Can you call back and MOVE your tickets from the second reservation to the FIRST reservation?
(You's cancel the tickets on the second reservation. Book for the first.)
You CAN book tickets that run past a given "end date" of a WDW resort reservation.
That way, you will KNOW you can use your tickets... AND, you could book FPs for that first day.