Passing Parameters to MSIX installed App

Hello, 

Apologies for so many posts in quick succession.  I have be able to get my application installed via an appinstaller calling an msixbundle. 

There is a file within the installation folder that needs to be set specifically depending on the user.  The only time I know who the user is, is when they download the appinstaller (each person goes to a unique URL to get the appinstaller)  I had initially planned to send an identifier as a parameter through the ms-installer link on a website, however due to security issues raised, the users will be downloading the appinstaller locally and installing from there. 

Does anyone know of a way I can get an argument sent through to the installed exe when the appinstaller is activated and the program installed?  It only needs to happen once to set the file?
I was hoping that there was some xml I can place in the appinstaller that would be passed through to the application as arguments, but this doesnt seem to be the case.

Many thanks in advance

John