It is not a crush washer. It is an aluminum gasket. It usually sticks to the plug head so hard that the average grease monkey has no idea that there is a replaceable gasket there. You can use a nylon or fiber, or aluminum, or copper gasket. All work equally well as long as they're the right size.
To soften (anneal) copper gaskets, heat them red hot and quench them in water--just the opposite of annealing steel. The copper work hardens after use, and annealing them gives another usage. As written in a posting above, new gaskets are cheap--buy several.
By the way, if you want to change the gasket without draining the oil, it isn't much of a problem. With the engine cold, and with a friend helping, remove the plug, put your thumb over the drain hole, the friend changes the gasket, and you replace it. You lose a coupl'a ounces of oil. Or your former friend goes out for lunch while you have your thumb over the drain....