Being able to change the preset media queries for different screen sizes by using the code snippet provided by Tom is surely a welcome addition. To take this a step further, the Advanced background menu (and perhaps also the Effect menu), should provide an option to write a customised media query. This would open up for things such as adding backgrounds specific for screen sizes other than the preset ones, as well as screen resolutions, device types, orientations etc. together with applicable syntaxes.
In addition to this, it would be nice to be able to add customised media query presets to the selector now called “Device”. This could be done using an option in settings, or perhaps this is possible by using a PHP snippet?