Editing default tor browser settings in whonix workstation dvm

How can i automatically set my security level to safest and choose an option for no script extension to show up on my tool bar? Following this(Disposable customization | Qubes OS) tutorial about customizing dispvms lead me to error 127 after launching ```
qvm-run -a whonix-workstation-17-dvm xfce-terminal

http://forums.dds6qkxpwdeubwucdiaord2xgbbeyds25rbsgr73tbfpqpt4a6vjwsyd.onion/t/change-default-preferences-for-tor-browser-in-dispvm-using-policies-json/16722