Allow us to decon items and save the guild slot as a "Spirit" (just like +1 to +5 bonuses), so we can reapply them to other items. Make it a high-craft ability to then turn it back into a slot shard, the bigger the slot, the higher the crafting required.
Also allow us to crunch smaller Guild Slot Spirits to make bugger ones. It would take multiples to create the next largest slot (like Siberys and Khyber shards). With guilds aging as they are, the lower slots are mostly useless to many of us, and become yet another vendor trash. Lets make them potentially useful for all guilded players, regardless of the relative slot size and guild size..
I recall some suggestions to allow us to craft special guild augment crystals with longer durations and/or more than one buff -- I would like to re-enter a petition for these as well. Ingredients would obviously include the GAC's purchased form the House K guild vendors.
Adding a guild slot to an item via crafting SHOULD NOT affect its ML.