[kh99]

Someone just asked about having a setting per forum, so maybe the same solution will work. Try creating a custom profile field with two choices, then create a new plugin using hook global_setup_complete and code like:

if ($vbulletin->userinfo['fieldX'] == 'somevalue')
{
    $vbulletin->options['legacypostbit'] = 0;
}

where you'd replace 'X' with the id of the profile field you created, and 'somevalue' with the choice that represents postbit. This assumes you have "use legacy" set to yes in your options, otherwise your plugin would check for the value that represents legacy and set the option to 1.