production question

Hi dear Blender community!
I’ve got very basic question. How can I tweak materials of the linked file?
It often happens that shaders are needed to be tweaked on shot to shot bases. I know that append command can be used instead, but this is not an option since during the production, assets go through continiuos tweaking, iteration and finishing, so by appending asset there is no way to update the asset. So how can I tweak the shaders in the linked rig?

I remember something relating to this in recent release notes.

Hi, Modron! Could you please give me some links to the info you’ve seen?

I could spend an unknown amount of time working my way backwards through the release notes, but then, so could you. Not trying to be a smart ass, that’s just the reality of it.

That’s fine, Modron. I’ve done some search but could not find the answer to my question.
People, my question is open! How do you tweak shaders in a linked character rig?