group messaging

Group Messaging.

When I turn off group messaging, and send a text to several people, is that the same as sending a BCC (Blind Carbon Copy) meaning no one else can see who I sent the message to?

Can I turn group messaging on and off within the same group?

How does turning group messaging on or off affect previous messages?

Can I turn group messaging on for just a specific group or does it affect all of my texts?

Thanks for your help