According to the NPS Yosemite site everything at the meadow will be open. Horses, store, gas station, etc. I strongly suspect the campgrounds will be open also. There may be a patch of snow here and there though.
If you have a reservation for the 26th of May the powers that be have declared the meadow will be fully functional then. Don't worry about it. Become a squatter if need be.
Old Dude