This video takes way too long to say what it needs to say and I am too tired to accurately summarize it. If anyone knows of a better video/guide, by all means.

Short version (probably lacking key details):

Need donor weapon with the desired stat up modifier, and the Igoshon shrine near the water temple. Equip the donor, cling to the wall next to the Lookout Landing tower, fast travel to the shrine. Head toward the gacha dispenser, crouch-walk up the stairs to the ledge on the right until Link's toes hang off the edge. Watch a memory, and mash A as soon as you hit the skip button. Repeat until the post-memory loading screen goes on longer than usual. Don't press anything until the menu loads.

Don't exit the menu from the point on.

Open the map, Link should be shown at Lookout Landing. Switch to inventory, equip the target weapon. Watch a memory. Check inventory Modifier should be transferred. Save. Load the save. Modifier should be permanent.

Once again, no freakin clue how these are found.