They can be devious and ask the ref to see if he thinks the yellow card might have been a red - then the ref can say that it wasn't even a yellow. Sneaky, but technically legal.What’s the story with VAR being used to over-rule a free kick and yellow card. I thought VAR was restricted to offsides, red cards and penalties. I think the refs have screwed up hugely here.
Edit: VAR can also rule on whether a goal has been scored (ball crossing line).
I thought they may also be able to use VAR if a card has been shown to the wrong player.
I don't know if a ref is allowed to ask for VAR if he/she thinks they have missed something or got it wrong (for example, if a player is claiming serious misconduct, the ref/assistants saw nothing, and VAR is not already checking that incident).
None of that answers your question or allows the actions you are talking about.