[kh99]

There's no option to do that. You might be able to use different postbit templates in different styles (i.e. copy postbit to postbit_legacy in one of the styles), or you could use a plugin. For example a plugin using hook global_setup_complete and this code:

if (STYLEID == 3)
{
    $vbulletin->options['legacypostbit'] = 0;
}

uses postbit in style 3 and postbit_legacy in the others (because I have "Use Legacy Postbit" set to yes in the options).