Return diapers?

Andie
My shower is Sunday and only 2 things have been purchased off the registry (of 50+ items all under $50, most less than $15) - and, as a Type A planner, I'm worried that I'm going to end up with a ton of diapers. We are using cloth diapers and already have several packs of disposables in sizes NB to 3 as backups, but I don't want to end up with a ton more if we aren't going to need them.
I'd prefer to return things that I don't need because there are still tons of things that we need before baby comes. After we are all set, I will absolutely donate diapers we don't use. 
My question is, if people don't include receipts, can I return unopened diapers for store credit? I've heard you can swap for sizes or brands, but I don't know what policies are on returns.
Thanks!