Once the diffuser reeds are totally saturated, the cells in the reeds eventually clog and lose their ability to pull the scent up into the reeds and throw the fragrance into the room. Therefore you need to replenish your reeds each time you refill your diffuser. Needless to say, you definitely can't move the reeds to a different scent of oil- because the cells will contain the previous scent.
Here at Emily Victoria Candles we offer a quality reed, to provide an excellent throw.