Besides all other modifications you are doing, please take note of the following

There are two important Server Actions in the Business Logic Module you might want to change

Profile_AddManualVerification

This action is used by this application to calculate validity dates of vaccination, recovery and tested. It used site properties for the various types. You might want to change that.

Profile_AddSelfVerification

This action is used by the Greenpass Track Mobile Application, when a user scans or uploads a QRCode. It does some basic validation. What it DOES NOT is to validate if a given certificate really belongs to that user. You might want to consider adding validation based on DateOfBirth AND last name of the user.