Dor

Aneesh
If there's a Forger like Shai who plausibly had an opportunity to ingest lerasium and become Mistborn, but she passed it up, could she create a stamp that makes her temporarily a Mistborn?

Brandon Sanderson
She would have to have access to enough Investiture to make that happen. The stamp saying, "Hey, I'm a Mistborn!" doesn't actually give her the Investiture to do that. She could rewrite her past so that she took that bead. She would not actually be able to use the power, until she got an infusion of Investiture, which could be done with a stamp in the right manner, but most of the time you're gonna have to have some external source. Basically you're gonna have to take a hit of Investiture, a large amount of it, and then use the stamp, and then it will feed on that to change you into basically any of the other magics.

Aneesh
Stormlight?

Brandon Sanderson
If you could get a hit of Stormlight, that'd work. The problem is, Stormlight's not easy to get off of Roshar, and it still is technically keyed. You could get it a lot more easily-- Stormlight would work fairly well, but what you really want is some pure, unkeyed Dor. That stuff, you could do all kinds of things with. But, you know, it's kinda dangerous. But that's the stuff you're gonna want, or something like unto it.

https://wob.coppermind.net/events/479/#e15205