Adjusting between Group & Single text messaging on Galaxy S4
In the stock messaging app: settings->multimedia message (mms) settings->Group messaging.
When this is checked, it will send a single MMS message to multiple people (all within the group), like in examples 2/3.
When it is unchecked, it will send a message to each person in the group individually, like in example 1.

All incoming group messages will come in as a group message regardless of this setting.  This setting simple controls how your messages are sent to a group.  As far as I know, however, you are not able to do this on a per message basis.