Digidesign does not support assigning passwords to an iLok Key.
You will not be able to register your iLok at iLok.com if it has been password protected.
If you attempt to use this feature, you should document your password. Make sure not to lose it as there is no way to reset it without returning the iLok to PACE. If you lose your password, you will need to arrange for this with PACE using the RMA (Return Merchandise Authorization) Form located on the iLok.com Support pages — in order to get an RMA number. PACE charges $10.00 plus shipping to remove the password from your iLok and return it.