Using common updatable worksheet for several Excel apps

[hbj]

My client wants to move an old Customer contact database written MS-Access to Office 365 Excel– simply because it is simpler than rewriting Access.
At the same time, they want to divide the database into three different worksheets/apps due to GDPR and because the tables have quite different structures.
I have been asked to move them to Excel, however I have one problem: I would like to use a common Zip code table for all worksheets. The Zip code table consists of Zip code, City and Country. In addition, there is also a country code table from where I lookup the country name based on the 2-letter country code in front of the international Zip code. The Zip code table should also be updated with new ones from all three apps.
Is there a way to open the Zip code worksheet in read-only mode, and only when the app needs to add a new line to the list, it will programmatically open in normal mode?
Are there quite other ways to solve this? Using SQL statements, Power Query, etc
/Håkan