it says that the person+ the people they consider themselves to be with (e.g. thei company) have changed the password, so that the password has been changed. Already (a signal word for Present Perfect).
2. the same as above really, only Simple Past is used because a specific point in time is given with "yesterday". I'm not 100% sure but I'd say it would be possible to say "We
Just a couple of observations. I agree with most of your explanations. I noticed a trend with the first word of your sentence which you didn't capitalize but you did in the middle of paragraph and with proper names.
Present perfect should not be associated with past time markers; i.e. ago, last week etc. I know people do say things like: "I have seen her two hours ago". It'