You must’ve made a mistake. Either you forgot to sudo, or you mistyped some directory name like vi /etc/udevx/file (udevx does not exist) or something along those lines.
Try again when you get a chance as root should be able to add/edit files anywhere under /etc.
I’ve actually done this exact thing (add udev rules) here: Yoga Pro 9i 16IMH9 has udev spam log while charging - What is the best course of action here? - #6 by j0rge