Combining Enchants

I want to say immediately that I don't mean stacking effects, as in putting 2 efficiency V enchants on a pickaxe.

My idea is being able to combine different levels of the same enchantment to get the max level of that enchantment. An example of this would be finding a Looting I book, and your sword already has a Looting II enchantment, by using an anvil, you can combine the book with the sword to get Looting III. 

Also, being able to seperate two enchantments from a book using a grindstone and another book. This should also cost experience points as well to keep it balanced. I say this because a lot of books that I find have two different enchantments on it for two different items. For example; I have found a book in a survival world that both Fortune II and Looting I on it. At the time I was still early game and having both of those would've been very useful, however I had to choose which one to keep because I wasn't able to seperate them.