Restrict Owner to List
Extends the restrict_owner option to allow specifying a list of users in trac.ini.
If you have any issues, create a new ticket.
Download the zipped source from here.
Enable the plugin and configure in trac.ini like:
... [components] ... restrictownertolist.* = enabled [ticket] ... restrict_owner_list= user1, user2, ...
Changed the settings variable. Use restrict_owner_list in ticket section.