Why i cant change 50_user.conf

I wanna to exclude some nodes but if i try to save it “permission denied”
How i can save my stuff in this file?

Not related to whonix, this is related to unix file permission.

If you follow the whonix tor config guide, you will see sudoedit is mentioned, this is because it requires the privilege to write on that file that the normal user does not have, but debian-tor or root has.