More specifically, editing the main /etc/sudoers file (through any means) may result in updates clobbering your changes.
But you can use visudo to edit any other file, and get its error checking capabilities on your other files:
visudo /etc/sudoers.d/mysudoers
BTW, when Apple discovers a conflict between their default config files and your customized ones, they always create a “Relocated Items” folder (in the /Users/Shared folder) as a part of the upgrade. You should see an alias to this on your desktop. Within it, you should find everything you need to manually resolve the conflicts.
- If Apple replaced a file, your original one should be backed up in there
- If Apple didn’t replace the file, their default version should be in there
In either case, I recommend comparing the live version against the one in Relocated Items and make any changes (to the live file) that you believe must be made.
I do this whenever an update creates a Relocated Items folder (and then delete that folder after resolving the differences). It usually only takes a few minutes (on my system, it always flags the changes I made to the Apache web server configuration).