Any way to disallow adminUsername for user xyz

So, I have created a new offer in the marketplace for a Ubuntu Linux VM and we are using an extra piece of software that uses Tomcat and a user xyz. This user was not very well named tho and our devs don't have time to change this implementation soon enough.
Is there any way do disallow the customers to use user xyz?
I could not find anything related in the [documentation](https://docs.microsoft.com/en-us/azure/templates/microsoft.compute/virtualmachines) and googling lead me nowhere.
If anyone has any experience with this, please share.

Best regards :)

The issue points to Azure VM templates and the linked Azure documentation, but names no repository file, test, or template entry point. First determine whether adminUsername can be constrained for marketplace Ubuntu images; done would require a documented, supported way to reject user xyz, which the issue does not currently specify.

Written by the indexing model from the issue text.