I pre ordered but my delivery isn't until October 5th so If I wait on line and get into the store and they actually have a 64gb in black like I want can I just cancel my online order and pick one up then and there in the store?
I don't think that would work as smooth as you want it to.
When you cancel, at a minimum your eligibility date likely won't reset automatically. You'll probably have to pay full price at the store.