I do not know why you would want to clear your XP, but if you do, kill yourself In-Game.
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Clear all the Minecraft folders on your computer and don't use the same Minecraft name :D
/ xp /kill /me / gamemode 1 those are the useful ones
Use Iron Ingots on an Anvil in Minecrafft 1.4+. (It requires XP)
By xp bottle you mean bottle o'enchanting. They cannot be made, but can be aquired by trading with a priest villager or spawning one in by creative mode or cheats.
There are mods for basically ANYTHING you can think of. Yahoo/Google or go to YouTube.