Hi, I live in Hawaii and was wondering if there are any downsides to grafting a cocktail avocado tree, with about three different varieties. Would the yields be affected? Ideally, I would like to graft varieties that would produce fruit all year round.

Look, it is done. You just have to be careful and keep the 3 varieties in the tree balanced. One variety will always try to grow more than the other. Get more sun etc. I don't particularly like it but if you have limited space you do what you can. I think is like having a woman pregnant with a child that is 7 month, another 3 month and another 10 months all at the same time. She does not have time to recover.   I would see more having a tree with two early varieties, the tree would have time to recover. I do know people that do it, my suggestion is to start with a large seedling 3 years old or plant the seedling and after 3-4 years top work it like I do in my video. so good luck to you.