I prefer to play games using borderless window mode for easy alt+tabbing around, but when I selected borderless window in ES2, the game window supersized and I can't navigate down to the options menu anymore (I have 2 monitors and a bit of the right side of the game window is now stretched over to my second monitor, and some of the bottom where the options button is is cut off). Is there a way to edit the game display settings in the game files somewhere or something?

You can edit the xml file in My Documents\Endless Space 2\Users\<number>\Registry.xml

Or you can just blow away the file and restart the game as well.

Thanks guys. I actually ended up fixing it by simply reorienting my second monitor to display below my main rather than to the side, allowing me to go down to the options menu and reset it. I'll take a look at that borderless program.