I don’t think this is true. In DF, you can’t do anything with excess AM or KPs. If you believe this vendor exists, post links. 99.999% sure this is not a thing.
In tWW, you CAN buy lots of things with excess Artisan’s Acuity. But just like in DF, there is NOTHING you can do with excess KPs.
As someone pointed out, you effectively get more AA when you get more KPs… so in tWW, you’re back to being able to buy stuff with that.
But directly speaking, there’s nothing you can do with excess KPs. I have like 800 extra KPs in DF professions. I only wish there was something to do with them. lol