With the introduction of the new Activity panel some of the rules and permissions have been simplified.

Many task fields can now be edited in all Task states.

Multi Actions selection (check boxes and top Actions menu) is enabled for Tasks only and applies to Author and above in the DeploymentTeam.  STP state rules apply in terms of being editable.

 Single Stage Actions menu is available for users of Author level and above in the Deployment Team.  STP state rules and some secondary rules apply.

Single Task Action menu is available to Users of Author level and above and in the Deployment Team.  STP state rules and some secondary rules may apply

Users of Author level and above in the Deployment Team can edit Stages and Tasks. 

The Approval lifecycle and state transitions of the STP remain the same.