Primavera P6 Assigning Multiple Resources to an Activity Part 51
You can assign multiple resources, roles, predecessors or successors at one time on the Activities page. Select multiple items in an Assign dialog box using Ctrl-Click (multiple discrete selections) or Shift-Click (multiple continuous selections) and then assign them all to an activity simultaneously.
This feature applies to assignments to an activity on the Activities page in the Projects section -- but not from the Resource Assignments page or the Resource Planning page.