AA's at any level or other ways to halt level gains

[starblight]

One ability I was surprised how often I used in Vanguard was the ability to halt all exp gain. Having the ability to stop level progression allowed me to keep a dungeon relevant until I was ready to move on. I would like to add some form of that into my server. At first I figured turning on AA exp would be a easy way too do this while at the same time still giving the player something for there kills. But I read on another post that the clients might stop this from being a option?

So is it possible to give players the ability to turn there AA experience on at any level? Whether it be with a command, UI, or a item? If not can I allow players to turn off exp gain altogether?

Edit
I had a thought and manually adjusted character_data >> e_percent_to_aa to 100 but at some point while playing I think after one kill the client sets it back to 0