I doubt it will be that easy, I don't believe Target will be able to do a direct swap for you on the return for the new one. You will likely NEED to order the new one online as an upgrade or new line for service on the first day it goes up for sale and wait a week for it to deliver on the day it actually goes on sale in the stores. To do this you need to be eligible for an upgrade on your line. Will be easiest on yourself to return sooner than later to avoid any issues later. Its a lot of BS hoops and crap to jump thru, I know, I been thru it way too much. Fiancee took my old iPhone when I upgraded, she activated a NEW line with my OLD phone. The Dbag at the store activated the line with a 24 month contract, yet told us she would get the discounted price and a contract when she was ready to buy a new phone. Seriously took me over a month back and forth with customer service to set everything right, and we still even had trouble in-store when we finally had it all straightened out and went to go get the new one!
Either way, right now is the worst time of year to be buying new Apple iPhones and iPods, as the fall announcements are only weeks away.