How might I make a shortcut for switching my macbook into airplay screensharing mode with my apple tv?
You mean the Available AirPlay Display icon that's on the menubar allowing you to opt to AirPlay whatever is on your screen to an Apple TV? It looks like a rectangle with an arrow at the bottom that is pointing upward. If you don't see it on the menubar, go into Display Preferences in System Preferences and toggle the option on.