First of all, thanks for an excellent and long awaited product! The last patch really did the trick with the LNAV drifting problems
Can you edit VNAV altitude constraints during the flight? I.e target altitudes for STAR waypoints?
Yes, in the MCU you can.
Use the 'cross at' button on the MCU to specifiy a crossing altitude at a specific flight plan waypoint.
After you press 'Enter', you will see the TOD display change to match the new crossing position. If in VNAV when you reach that crossing position, the TOD will automatically revert back to the destination's evelation from that altitude.
The limitation on this is you can only specify 'one' 'cross at' point at a time.