Unless there is a sale for 69% off hookers and blow on the 72 hour layover of the all inclusive in the Caribbean, this is probably a poor idea. You don't even get credit towards reserve guarantee for YS flying on an XX day. It is truly flying for free unless as previously mentioned, you're already full (or plan to be by the end of the month, I think).

What equipment are you on? If it's the 717 you can't move XX days but you could always GS the trip. GSing with RES days in the mix is typically a good deal for the company but if you really want the trip, you'll be paid for block and DH on your XX day and get a PB day -- all credit will be put towards reserve guarantee. If you're on something a bit more stable like the ER then move your XX days around so the entire trip is during RES days and this way you'll be working off your guarantee and hopefully putting yourself into bucket 2 for later reserve considerations.