Lets dispell some of the incorrect information posted on this thread.
a) you will not be classified as a 'thru hiker', therefore you WILL need a permit. No exceptions.
b) You can only reserve at a shelter that still has space. You may need to plan longer and shorter days than originally planned if any shelter on your schedule isnt available.
c) IF the shelter is full, then a thru hiker allowed to camp within sight of the shelter. Since you are not a thru hiker and have a reservation, you will need the shelter to be full, and have a thru hiker come in that is willing to take your spot so you can camp.