You cannot send your racquet back with your demo order and as El Diablo mentioned we cannot include it back with a new demo order. We can however do this, if you send the racquet to us to string, we can ship it back for free.
As far as demos being requested on a certain day. We can make that work if you call in to place your order. However we ship our demos out Ground so please allow 5 days from when you place the order (assuming racquets are in stock). If you want the racquet on a certain day quicker than that, you can pay for 2 day shipping.
If you have more specific questions about a demo order, please call in to our customer service and they will be happy to help.