If you event.setCancelled(true) in the PlayerInteractEntityEvent (or even in PlayerInteractAtEntityEvent) to prevent a player from breeding an animal or changing sheep wool color, it still looks like the event happened to the client.

Meaning, if i click on a sheep to change wool color, i see the new color on the sheep. But when i reconnect the sheep is back to the original color meaning it was not actually changed server side.

If i click an animal to put them in breeding mode, i can see the hearts over their head, however they do not actually breed and no baby is spawned.