If
your account is an admin account, the other user can't access your account without your account password, unless their account is also an admin account.
And, if you both have your accounts set as admin accounts, then each of you can change the password on the other account, and each of you can change the account level for the
other account.
You don't need to know the password - all you have to do is change it (reset password in the Users & Groups pref pane)
So, you can change the
other account password -- because you have an admin account!
You can
also change that other account to a standard account, because you are now an admin, and the system will allow you to modify the other account.
So, if you are both admins, using the same Mac, you two need to decide if you really need to "mess around" with the other user account. That goes both ways.
Whoever is admin on a Mac has the "keys to the city"...
You two will need to agree about who has access, and also agree about not changing the settings on the
other account.
If you are both admins, then that would be on the honor system.
