Create El Capitan install partition
Try to return everything back:

diskutil resizevolume disk0s2 R


and then:

diskutil resizeVolume disk0s2 480G jhfsx InstallOSX 10G



  Resizing a volume that is currently set as the computer’s startup disk
  will invalidate that setting; use the Startup Disk System
  Preferences panel or bless (8) to reset the resized volume as the
  startup disk.