As long as the bunnies previous diet wasn't causing health issues or poop issues, it's always best to keep a new rabbit, especially a baby one, on the same food and diet they were used to for the first couple of weeks in their new home. And don't limit the pellets for baby rabbits as long as it isn't causing mushy poop problems.
Changes of food can be stressful for rabbits, especially baby ones. It's not good to be changing the food of a recently weaned baby rabbit unless the food it is getting is making the baby sick and/or causing it to have digestive problems. The owner should stick with the exact same brand and type of pellets and the same veggies the baby is already used to eating. Then after the baby has settled in after a few weeks, if they want to change the pellet type/brand, that can be done gradually over 2-4 weeks time while gradually increasing the new pellets while decreasing the old. New veggies can be then tried after the pellets have been switched, starting with one new veggie at a time and gradually increasing if it doesn't cause digestive upset.
Also with alfalfa hay, some rabbits and baby ones, can be sensitive to it suddenly being introduced into their diet, so it's better for them to gradually introduce it into the diet if it's even needed. Like majorv said, if a good alfalfa based pellet is being fed, alfalfa hay isn't necessary and can make the diet too rich and high in protein, more than is needed. A good quality grass hay(no mold, no noxious weeds, not dusty) would be better when a good alfalfa based pellet is already being fed, and grass hays can almost always be given right away to all age of rabbits and in unlimited amounts without causing any digestive issues.
