I checked the config file and what has been included is to use a different prefix for the User table vs the other tables of Q2A so you can share users between two installations, nothing more.
If you wish, you can define QA_MYSQL_USERS_PREFIX separately from QA_MYSQL_TABLE_PREFIX.
If so, it is used instead of QA_MYSQL_TABLE_PREFIX as the prefix for tables containing
information about QA user accounts (not including users' activity and points). To share a
single user base between multiple QA sites, use the same values for all the QA_MYSQL_*
constants in each site's qa-config.php file, with the exception of QA_MYSQL_TABLE_PREFIX.