Yes.  The process would be very similar to this post:

In your case you’ll be changing the supervisor field instead of the username.

Let me know if you need more info.

Ed

Does this work to update an additional field? I tried to do this but it took it as me uploading new users. 

Yes absolutely.  I use .csv files daily to make such changes in about 10 additional fields that we manage.

You need to use the username field, or the Unique User ID to “name” the accounts that you want to update. Additionally, you need to check the box for “update information for existing users.” If you aren’t changing branch information, then you can kinda ignore the sub question.

depending on the number of users you need to update and whether the update is the same for all, you can also select them all on user management page and then on the bottom right, choose Edit Users. I use this frequently to do mass password updates.