Good question. 
If I remember right, you previously said, that calamares gets confused by user user already being created during live boot. Therefore you manually deleted account user user before creating the iso.
Therefore we concluded that user user should be created during first boot of Whonix rather than during build of Whonix. However, also in live mode user user creation should not be done by Whonix anon-base-files.postinst but by calamares.
I guess what I am asking is, is it possible to make calamares not get confused by an already existing user user account?
What’s the name of that user account? user user? I guess not? Probably live-something? That should not really matter since it does not interfere with anything.
Yes. Ideally that would also be left to anon-base-files.postinst?
Currently for non-live Whonix builds as per git master anon-base-files.postinst creates user user with --no-create-home, uses pam-auth-update --enable mkhomedir, thereby populates the home folder on first login.
Also anon-base-files.postinst locks root account as per Restrict root access for new builds by default so calamares don’t need to ask about root account either.
I don’t know the calamares requirements and how we could design this interaction. Should we support users choosing arbitrary user account names in the installer? Self-chosen passwords right in the installer or enough after they login first?
So the more calamares (except for live-something user in live mode perhaps?) can be configured to stay out, the easier it would be from the Whonix side. Otherwise anon-base-files.postinst user user creation part would have to be converted to a systemd unit file which is more complicated.