No its not.
rejoining is illegal if you gain levels from it. if you're on level 2, go to "change a setting", come back and you're level 6...not good. if you leave on 6 and come back on 6...that's fine.
if you do rejoin and gain no advantage but someone wants to punish you for it anyway, tell them you gained nothing. the reasonable ones (like me) will take your word for it. beware though, punishment will be increased if you lie about that.
Through the darkness of futures past,
The magician longs to see
One chants out between two worlds:
Fire, walk with me.