Would be helpful if the "Display Settings" section (the one where one can configure screen resolution and related stuff) would have a button to test the changes before applying them, in the same way as e.g. MS windows - that is, one sets a new display setting (e.g. testing a different screen and resolution), clicks "test", it changes to the new settings for 5 seconds or so, and then comes back to the old setting.

This would be especially helpful in settings in which some change could result in an invalid display that does not allow visual cues to revert - for example, in my own setup, if I try to switch to a laptop screen after another screen is already running on HDMI, it shows only random noise on the screen, so I cannot click back on 'reset' to change the settings (this is a mesa bug so unrelated).