I was thinking that it can only be done if you reach lvl 120 and it will be available for unlimited period and unlimited tries yes. If you think about it, a player might have only one character in the game, so it makes sense to let him/her try different abilities, for a PRICE. And make no mistakes, 2000 nuggets is close to 40 euro ... that's not something you throw away lightly. As for the rich kids for who 40 euro is the price of a toothpick, well what can we do about those anyhow? They already have the best gear, all special items and they are spinning the world around them anyhow, especially in a full premium world. But, these players represent 2% of game's population? There is nothing to be done about them in terms of unbalancing the game, but what I see in there is that for a price of 2000 BONDS a normal player might turn his/her world around and try something else. and THAT is not an abuse in any sense.
Remember, my idea presents everybody in a class-less environment. I am sure there will be nicknames for certain abilities, especially concerning fort battles, but otherwise a player can remain a blank canvas to the rest of the world. Which doesn't really matters either, it's not like you didn't duel a player just because his/her class is Soldier or dueller. I do not make distinction in classes when I duel people, the only distinction you see is in fort battles and maybe when you are dueled by a dueler and he/she's not at your location (dueller).