I was wondering if there was a way to add enchantments (using commands) to an already enchanted item. For example, I have a command that enchants an item if you have enough levels, but what if you get enough levels and you want to enchant it further, such as the item having protection I but the person wanting to upgrade to protection II or protection III? (I am making an zombie apocalypse map on vanilla and do not want to use mods.) Would there be a way to remove the enchantments and then add them back on the higher level?
Basically, just enchant the item again with the already enchanted item on creative. You can't double enchant items in survival as far as I know, so this is the command;
/enchant (your username) (enchantment) (level)
Just do that twice, and you should be able to have two enchantments at once! (tested on 1.9)
you don't need a command - just get each desired enchantment individually on separate tools/weapons/armor, then combine them with an anvil to get the combined enchantments. you can also use enchanted books and combine them with the tool/weapon/armor with an anvil to get the enchantment you want.
i hope this helps!