I agree that it seems clearly inappropriate, but I'm not sure if it's actually actionable.
When do we define the tournament as having started?
- If it's once the players sit for round one, then this behaviour is legal.
- If it's sooner than that, then this is illegal, but so are plenty of other Regular event type behaviours that we presumably wouldn't want to stop - such as the “pick a box” mentioned above, or players lending newer people decks at the last second, etc.
Of course we can have a word with the player in question about how appropriate their behaviour is, but I don't see how we can do anything beyond that without breaking consistency.