Their feed consumption is already pretty minor per bird, and most based on protein requirements. You can add greens and your quail will love it, but mostly they consume the gamebird food for the crude protein. Also if you add greens you must add digestive grit. Gamebird food is water soluble in their digestive system so they don't need grits. To digest anything that wont' dissolve in water they have to have access to grit. Oyster shell does not qualify as digestive grit.
Hens do need oyster shell fed to them freely. They instinctively know what their mineral requirements are and won't eat too much of it. Oyster shell runs me like $10 a 50lb bag and that bag lasts me quite a while with 30 hens.
how do you deliver the digestive grit, on the side freely or mix it with feed? In Georgia we eat a lot of watermellom and I put the rinds in the pen and the birds absolutely love it. Problem being afterwards their poop doesn't fall through the 1x1 wire on the bottom of the cage. It becomes little balls and sits there. I've discontinued this treat out of fear it constipates them. Maybe they just need grit and if so my birds thank you in advance!
With grit i'd recommend feeding it in a feeder because they will just take dust baths in it otherwise. You have no worries with watermelon rinds I've been feeding them for years, oversized feces isn't a huge concern unless you see bloody stool. The size difference is most likely just due to the change in diet from what they ate the day before to having the rinds.
