If UA forcefully downgrades someone can't you push them to put you on another airline (LH, LX,..) in your ticketed travel class?

I've flown GF a couple of times on award tickets and always before I travel I research options including other airlines in case my flights are cancelled or downgraded. If they were I would request/push UA to put me on my preferred alternate flights for which I also track seat availability pre-departure. Fortunately I've never had a problem but from the advice I've read here my motto is "be prepared".