I can edit a constraint from the TA if I click on a constraint in the timing report or select and right-click "Edit Source Constraint" while a constraint is highlighted in the Timing Tab. However, if I edit a constraint in this manner, it implements and attempts to edit the constraint again, but the following Error appears:
"Failed to Edit Source Constraint"
The work around is to exit and then restart Project Navigator.
This problem will be fixed in 11.1 version.