I probally don't understand you right but you Simply probally need this Information to go forward: SEBLOD Multi Site has settings for user Permissions if you set the titel and so on look at the right down corner and there is a sign for permissions you choose a not logged in user that gets logged in if your not logged in its called guest user ^^ so you need in you template or mod a way to say the user with ID for example 811 is the guest user so you simply set the ID to 0 in the script for Compatiblity. so you need to add simply some lines of php like
$userID = $user->get('id');
if ($userID == '866') $userID = "0"; // ds_changed
then you can make the same check on the if show logged in msg and if logged of MSG with the PHP var $userID you don't use the original $user->get id var and overwrite it coz then it comes to the fail that the user 0 simply has no access to the page ^^ coz he is not the selected guest only user of the multi site.
this is enought if you modify the modul directly and you can assign moduls to diffrent sites with the access lvl simply give the modul a access level that applys only to one site.
hope that could help a bit since i don't realy understood what you exactly trying to do.