Switching resolutions on a Retina MacBook Pro usually requires going through System Preferences, but an app called QuickRes is designed to mitigate that annoying process.
QuickRes puts an icon in your Mac’s menu bar that allows you to quickly jump between a variety of preset display resolutions, even beyond supported by Apple, all the way up to 3840×2400. QuickRes can also enable HiDPI mode on non-Retina Macs, effectively doubling the resolution and giving a clearer (albeit bigger) picture.
To switch resolutions, you can right-click the app’s menu bar icon to select which display you want to change (if you have more than one), then select a resolution from a list of presets. You can also setup anywhere from two to eight of your favorite resolutions and switch between them quickly by clicking on the menu bar icon.
QuickRes is available in two flavors. The paid version is available for a 9to5Mac-exclusive price of $.99 (regularly $1.99) through this discount link. The free version, which supports fewer resolutions and does not include a quick HiDPI toggle for non-Retina, is available on the Mac App Store.