I've tried that, and unless it's already discounted it won't work. I very much doubt if the distributors to independent off licences work on a sale-or-return basis.
I once brought back an expired bottle of beer to a well-respected Dublin off licence: it had been expensive and when I got it home I noticed it was ludicrously out of date. It was the last bottle of that particular beer in stock, but they let me exchange it for something else. When I was next in, some months later, the very same bottle was [i:3ttj88dm]still[/i:3ttj88dm] sittng there.
As far as the shops are concerned, if you're not going to pay full price for elderly beer, some other mug will.