Alert:
I have typically used a non-user in the 'viewer' role access only, for obvious reasons. What you are trying to do can be done, provided you have to control all other tables and fields for viewing access only to these non-users. And, in the future, if you wish to share the app with another non-user or a group of non-users, you are limited to going with what you have already done on this non-user role - meaning they will also have option to edit what you want this non-user to edit.
Steps:
1. Connect the tables - meaning connect one field from the existing field as the reference field to this new table and pull all other necessary fields as 'look-up' field for viewing only purpose
2. Create new fields in this table that needs to be edited by the non-user
