downgrading a mac os system on a new mac

preparing a macmini as an izzy installation machine:

since the macos x installer would not work on a newer system, a work around is to reshape your drive partition with disk utility and add a 8 GB sized partition for the installer. Using the createinstallmedia command from Apple ( an installer can be created on your HD / SSD. Problems during installation with slow, faulty USB Sticks are gone and afterwards the partition could be used as a 2nd boot option for the terminal / diskutility or be erased.