I recommend adding seven new recipes to the Stone of Change that allow augment slots to be added to randomly geneerated loot. Each recipe would add a different color augment slot to an item, raise the minimum level, and cost a combination of some amount of Tokens of the Twelve, collectibles and an actual augment of the desired color.

Only one augment slot of any given color could be on an item. (Can’t add a yellow slot to an item that already has a yellow slot.) And an item can have no more than two augment slots total (whether they were on the item when it was generated or subsequently added via the Stone of Change). Level increases would be cumulative (i.e. if you add a Colorless slot and a Green slot, it would raise the minimum level of the item by 4, assuming the level increases listed below.)

Examples/recommendations:

Colorless Augment Slot:
Requires: 5 Tokens of the Twelve, 10 common collectibles, 5 uncommon collectibles, any colorless augment (i.e. Diamond of Dexterity +2)
Min level increase: 1
Item type restrictions: None; can be added to any randomly generated item

Blue Augment Slot
Requires: 10 Tokens, 10 uncommon collectibles, 5 rare collectibles, any blue augment (i.e. Sapphire of Good Luck +1)
Min level increase: 2
Item type restrictions: Armor and shields only

Yellow Augment Slot
Requires: 10 Tokens, 10 uncommon collectibles, 5 rare collectibles, any yellow augment (i.e. Topaz of Proof Against Poison +6)
Min level increase: 2
Item type restrictions: Accessories only (bracers, trinket, ring, cloak, etc.)

Red Augment Slot
Requires: 10 Tokens, 10 uncommon collectibles, 5 rare collectibles, any red augment (i.e. Ruby of Improved Flame)
Min level increase: 2
Item type restrictions: Weapons only

Green Augment Slot
Requires: 5 Greater Tokens, 15 uncommon collectibles, 10 rare collectibles, any yellow augment, any blue augment
Min level increase: 3
Item type restrictions: Armor, shields and accessories only

Orange Augment Slot
Requires: 5 Greater Tokens, 15 uncommon collectibles, 10 rare collectibles, any yellow augment, any red augment
Min level increase: 3
Item type restrictions: Weapons and accessories only

Purple Augment Slot
Requires: 5 Greater Tokens, 15 uncommon collectibles, 10 rare collectibles, any red augment, any blue augment
Min level increase: 3
Item type restrictions: Armor, shields and weapons only

Special consideration: Using the examples above, you would be able to add an orange slot to accessories, thus allowing someone to slot it with a red augment. An option for this update would be to allow monks to use rings with orange augment slots to add damage / metal types to rings (similar to the way Tower of Despair rings work). However, adding a red augment to an orange slot on other accessories would not give any benefit. Nor would red augments added to rings give benefits to anything other than handwrap melee damage. Therefore, the only benefit to adding an orange slot to a non-ring accessory would be to add another yellow augment to an item that already has a yellow augment slot.