virtualbox.org

I love VirtualBox's handling of multiple displays, except for one issue: I'd like a way to enable/disable a display on the fly. From what I can tell there isn't a way to do this. If I start the guest with two displays, and then disable one in the guest, it automatically gets re-enabled. If I start the guest with one display, I don't see any way to add a second while it's running. Is there any other way to shift between single- and dual-display on the fly (without rebooting the guest)?

Sorry, you can't do that. The Guest Additions are responsible for the displays and they initialise on boot. The VM settings for the monitor count is also unavailable as long as the VM is running. It has to be in shut down state to change it.