[Oblivion Knight]

How to get this working with EITHER postbit or postbit_legacy as default.

Move the plugin to use the hook cache_templates, and replace the code with:

global $vbulletin;
if ($vbulletin->userinfo['field5'] != 'Use Forum Default')
{
	if ($vbulletin->userinfo['field5'] == 'Horizontal Postbit')
	{
		$vbulletin->options['legacypostbit'] = 0;
	}
	elseif ($vbulletin->userinfo['field5'] == 'Vertical Postbit (Legacy)')
	{
		$vbulletin->options['legacypostbit'] = 1;
	}
}

Add an additional option to the custom profile field at the TOP of the list, "Use Forum Default".

This should work on both 3.5.x and 3.6.x setups..