New -> Shortcut, then enter your command. You can then create a hotkey for that shortcut by modifying its properties.
Behind the scenes, LIV registers itself as a URI Scheme handler for the liv-app “protocol”. When Windows is asked to execute a URI as a shell command, it will look for a registered handler, and then start that program. When LIV is already running, a second instance of LIV is loaded - it then sends the command to the first instance of LIV before closing itself. Naturally, this process takes some time. We don’t recommend using this interface for high-frequency control of LIV.