Database user naming policy (mysql and postgresql)

OS type and version Ubuntu 18.04
Webmin version 1.973
Virtualmin version 6.16.gpl

In August 2021, we made an update to webmin and virtualmin. We upgraded from webmin 1.955 to 1.973 and from webmin-virtual-server 6.12.gpl to 6.16.gpl
A year later, we realize a big change in the automatic creation of associated databases when creating a new virtual host. Before, for a user of the “firstname.lastname” type, the database username remained “firstname.lastname”, since the update, the database username becomes “firstname_lastname”.
This gives us very big management problems in our infrastructure. Could you tell us which file(s) to patch to revert to the old behavior, and even better, how to patch it(them) ?