I've read ceramic eggs are a good choice so they stop trying to open eggs. Make sure nests are cushioned, as if an egg cracks they almost always eat it. I've also read of some people emptying an egg through a hole, then refilling it with nontoxic orange colored dish soap to create a negative association with the taste. You can also buy nest boxes that roll eggs into a covered area.
While sometimes it's just an "eggs are yummy" thing, sometimes egg eating is a sign of nutrition deficiency. What are your birds eating? Are they getting enough protein and calcium?
Trimming beaks is a medical need to me, for crossed beaks. Remember a bird's beak is like it's hands. Trimming beaks short is an extreme act, usually only done in factory cage farms. I've never heard of trimming beaks to stop egg eating.
