Changing locked Safari Home Page on El Capitan and higher OSX when everything else fails!

Open Terminal via Utilities folder on your Mac and enter following command:

sudo dscl . mcxset /Users/USERNAME com.apple.Safari HomePage always -string "ADDRESS"

Substitute USERNANE with your actual home user directory name and ADDRESS with URL of website you want to set as your home page... Type your user account password to execute.  

Reboot your Mac!