Unfortunately you cannot get any patch version earlier than the latest version. Going forward, what you can do is archive your installation so that you may roll back to a previous version if ever needed.

To do this, click the Impulse orb in the upper left and then click 'Preferences'. Click the 'Archive & Install' listing on the left. You can toggle Impulse to automatically archive your install before downloading new updates. If you wish to do it manually, you can right click on the game from the 'My Games' tab and choose 'Archive Application'.