Dumb question: How do I get to set playtest art on a per-card basis?

[Sgt. Cookie]

Rather than the all-or-nothing option of Playtester Art mode, I've seen some people set the art on a per-card basis. How do I do that?

[󠀡⁧⁧󠀡]

compendium > card lib > click a card > see bottom

[DuckSonata]

You can also right click cards at various points in game (when viewing your deck, at card rewards, in shops, etc.) to get the same options pop-up.