How to change character archetype using Osiris

I'm using True Companion mod that makes AI take control of my party in combat. I would like to make my own tweaks to the mod and my question is, does anyone know how to change a characters archetype using Osiris?

I know there is a variable in DefaultCharacter.charScript that sets the archetype:

Code

EXTERN ARCHETYPE:%Archetype=base

I read from https://docs.larian.game/ that you can access and change any global variable using Osiris.

I've tried:

Code

SetVarFixedString(_Character, "Archetype", "NewArchetype");

But I'm not quite sure if it's correct. If anyone has any tips here on how to approach this, I would like learn more about this.