This suggests the option to go under gameplay settings and switch on or off "experience freeze".
If you battle while experience freeze is on, you will not earn experience from battles. Quests? Maybe. That could be an additional setting. I was thinking about this on my main wizard who is level 50. Eventually I want to level up all the way to 100, but for now I want to be the best level 50 and go into PVP. I also want to hatch pets but I need gold. Farming, fishing, collecting materials is alright, but somewhat slow. The best way for me to farm gold is to battle monsters and sell their drops. But if I battle for just half an hour I'm pretty sure I'll level up and I don't want to leave my level range yet. This suggestion might be selfish in its inception, but I'm sure that there are others who want to be better within their own level ranges, too
I very much want an XP Freeze feature. I think it could be implemented with minimal consequence, but probably should come with a warning attached just for good measure; something like "This could make it very difficult for you to complete future worlds, are you sure?" should suffice.
Farm for items on another wizard, garden, fish... there are plenty of ways to get gold without getting XP. If you freeze XP like this it should remove the ability to get XP for that dungeon/quest forever along with any quest rewards. You only get 3xp per pip used for battles, you will not level up in a half hour from farming instances that you have already done. You shouldn't be allowed to get spell quest rewards while avoiding the XP given.