That isn't a particularly viable option,WellIf i've difficulty with a boss I can simply respec to be more deadly against him and then respec back to my previous character and continue the journey.
Is not a game breaker but in my opinion it weak the risk of the PVE in Dark Souls 2
the items are consumable and very rare, current streamer is at SL 84 and has only found 2. In addition he hasn't even found the npc that allows you to use them. Even if you really do need them to respec for a single boss and respec back, it's unlikely you'll be able to do it more than once or twice per game without knowing exactly how, not to mention not having upgraded gear for whatever class you respec to in the first place.