Even if I don't know the incomes the company has because of this mall item (cursed doll) and even if this suggestion affect the economics of the company I will still suggest this.
I was thinking at first to make the anti-experience option like a simple button next to the skillbar and not as a wearable item that expires. At least for the first month this option should be free because there won't be many guilds to join and many of us would want to stay at a specific level. As we all know, to donate exp to a guild every 5-10 minutes is pretty annoying and even with the cursed doll, sometimes we forget about it and also it uses one of our free slots so we can't use at the same time glove and wind shoes+ and we have to switch every second... Also if you accidentally level-up there is no coming back... It would be so nice if the anti-experience option was free but if this isn't possible at least don't make it free BUT change the wearable item to a button option or something like a check box somewhere and we could activate that option via item-mall. I'm not sure but I think I saw this in another P server (don't remember name and how was it exactly). I hope you got what I mean.