some usergroup questions

[BigJohnny]

I have some questions about using usergroups as secondary groups.

First of all does enabling "Can override primary group title/markup" affect all of the options, or does only the html markup/username get overridden?

secondly.... if the primary user has more fourm viewing permissions, than one of their secondary groups, will the secondary group(s) override those permissions and deny them access/posting rights that they already have?

I have a regular members group, and a VIP group.

I want to add an adults only group for access to some adults only forums/categories. But i want to be able to apply it as a secondary group for both regular members and VIP members, without affecting those groups current permissions, other than a user title change.