There could be an Augment to create rune slots on an item that has no rune slots (Of course it will only be for Amulet, Armor and Weapon. The default items.) and another Augment to increase the amount of rune slots in an item. item you already have (For a maximum of 3 slots).
With that, it would be cool, creating the possibility of using Runes on Unique items that don't have a slot for it or any other item you like and want rune slots on it.

Augments could have a failure rate depending on how they are being used.
For example, by the combination menu (G button), there would be a 50% chance of the Augment breaking and not changing anything. (Only the Augment would break, the item would remain intact!)
But when using on some table, the workbench for example, would have a 25% rate of Augment breaking. (These numbers are just examples.)

And Refined Augments would have a lower failure rate.
That way, you could balance the way you wanted, even if you managed to pick up multiple items.

In my case, I had Lucky Charm 5 and at Fort Joy I got countless Augments, it was really easy to get them.
I could just sell the ones I wasn't going to use and make some easy money.
Before finishing Fort Joy I already had more than 30 different Augments.