As things stand now, once you put a guild augmentation crystal into an item, it stays there until six hours expire and that's that. Sometimes this is inconvenient. If you are about to enter Ritual Sacrifice with only 30 minutes left on the crystal, you know it will run out before the final boss fight, but there is no way to renew it now. And I suppose there may be situations where there is plenty of time left on a crystal, but for a particular quest you'd like a different one. (This one is hypothetical; Ritual Sacrifice was my real example.)