Changing 16/9 size to a square format within blueprint

I am looking for a console command line within my level blueprint. So I can change the image size of the game. I have a 4K projector. At the moment the game runs at fullscreen, but I only need to have a square image like 2160x2160 with black boarders left and right. Is there a simple way to change it with a console command line, without touching camera settings? And I guess, it would be best to still send a 4k resolution to the projector.