If you need to find a one-time substitute for a shift, please email all of the Music Library staff - including the full time staff (i.e. not just students), so that we know that there's a switch being made. Everyone needs to keep in mind their own limitations on hours - TAs/PAs can't work more than 10 hours a week beyond their Music Dept appointment, others are limited to 25 hours/week.
If you want to try to just make a swap with one person rather than involve everyone because you suspect that they have the time free that you're looking for, that's fine. But please still CC the full time staff.