Hint 1:
The master keycard won't give you the right to override access settings. It is used for calibration - to ensure the arm gets the documents that are requested and not, for example, the neighboring documents, wink wink.
Hint 2:
You need to mess with the system to get you the document you need (the blueprints) when you request the document you can access. For that, you need to miscalibrate the arm in a specific way.
Hint 3:
Find out the storage numbers for the blueprints and the will.
Hint 3.5:
Hack into Johnsen's computer.
Hint 4:
You need the arm to point at the blueprints when Johnsen requests the will. So, when the calibration system requests to be pointed at M20, you need to point it at ...?
Hint 5:
blueprints# minus will# = the number you should point the arm when miscalibrating minus M20