How to restrict usergroups from using certain functionality?

[Opserty]

the recommened way of doing things is using is_member_of() as it checks additional usergroups and also means that your code won't break if vBulletin change the usergroupid column name (obviously they really wouldn't but it is just an example of how it could break).

I didn't understand what half of your post said though.

$post is used in the postbit(_legacy) template so it won't have any effect in the MEMBERINFO template.

$userinfo or $prepared (3.6/3.7 respectively) are the variables in use in the MEMBERINFO template.

$bbuserinfo is the variable for the user that is currently browsing the page.