Follow these steps:

That should get you to the Room Separation line entry in Visibility / Graphics.  Then, you can:

  • press Spacebar to toggle visibility on / off
  • press Right Arrow, then Spacebar to open the Override sub-dialog

As you probably know, I’m a big believer in Keyboard Shortcuts.

However, in all honesty, if you have mouse and are using Revit 2013, it is probably going to be quicker to:

  • Select a Room Separation line
  • Right-click
  • Override Graphics in View – By Category…