Once you set the "PC Programming Password" in the General Setting dialog and write to the radio, you have to input that password every time you attempt to read from or write to the radio. If you change it from the default (which is set to nothing/null at the factory) and forget the password, you've essentially bricked the radio, at least from the perspective of editing or updating the codeplug.
It's a deliberate design feature to safeguard the privacy keys. Otherwise you could "borrow" a radio programmed to communicate on a secure network, read the codeplug, and clone any number of additional radios that could listen to all the encrypted talkgroups.
There is a separate "Power On Password" that can be required on startup, which does not have to be the same as the PC Programming Password. It can be changed by reprogramming the radio, but that requires you to know the PC Programming Password.
If you lose the programming password, you can't read or alter the radio programming. If you lose the power-on password, the radio is a brick.
Turning the radio on while holding down PTT and either the top or bottom side button (I forget which) puts the radio in a special boot mode where you may be able to overwrite the old code plug with a new one and wipe all the old passwords and privacy keys.
