How to change appearance in Sekiro?

I was stumbling upon this speeedrun video, where the character looks totally not like the default one. So I was wondering how I could change my look as well. I couldn't find anything within the game about this. Also my few searches on the web were not successful.

How can I change the appearance of Sekiro?

Do I need to tamper with the game files (like renaming files)?


It appears to be ZullieTheWitch's Costume Pack Mod.

Screenshot for comparison: Screenshot of a modded player character in Sekiro