Matt Tillman

Yeah variant sets aren't strong enough to apply if there's an existing local opinion, even for in-memory layers. So if there's already a material assignment you can't assign a new material with a variant set.

There's a couple of workarounds I briefly cover in this video:
https://youtu.be/k-S-MUp6ea4?t=21m6s [youtu.be]

Basically either only author the opinion in the variant set or clear the existing opinion with python (only works for in-memory layers).

Sounds like a classic LIVRPS [lucascheller.github.io] issue.
There's a strength hierarchy for composition arcs. Local (or sublayered) opinions are strongest. Variant opinions are stronger than References, which is probably why referencing worked but sublayering didn't.

If you dive into the Component Builder nodes you can see they have notes in there about how they set up material variants to avoid LIVRPs issues.

You can jump inside the layout LOP and change the asset references in there.
Here's a test replacing pig heads with tommys