how to prevent the built-in administrator to change its password?

Hello, press start button, type Computer management and run as Administrator
expand node "Local users and groups", double click on Administrator and check "User cannot change password"

mfran2002 said:

Note: I should have to do it only for the built in admin (not for all the users) to prevent unintentional damages from users...

Standard user accounts cannot change Admin user account passwords anyway so you do not have to bother doing anything to protect it, just leave it in its original condition and disabled.
Change account password - TenForumsTutorials

Denis

If there are other administrators (you said some IT colleague) in addition to you, then only you 2 can change the password.
This means you 2 need to set password for the builtin admin and not share it with anyone.

To set new password enable built in admin, uncheck "password never expires" and check "user must change password at next login".

Any other users that are administrators can do what ever they want, if you want to prevent this make sure they are not admin.

Admin does not have any restrictions.
If the problematic admin is causing trouble you can't stop them except to limit their account privilege.

there is no registry hack to limit what admin can do, because they may edit the registry as well reverting your settings.
You either trust your administrators or you don't.

mfran2002 said:

unfortunately I can't disable since it is used by some IT colleague of mine

1 Then tell them to stop using it for any purpose other than that for which it was created.

That purpose is [only] to be enabled automatically by Windows at the Safe mode login screen if Windows detects that there are no other functioning Admin accounts on the computer.

mfran2002 said:

It happened that one (skilled) user changed that pwd without inform anyone and then forgot the pwd...

2 Make your other users Standard ones not Admin ones. You cannot stop an Admin user changing passwords. Only you and, at your discretion, a small number of trustworthy others should be Admins.
3 Remove the password as shown in the tutorial.
4 Disable it.

Best of luck,
Denis

mfran2002 said:

in the end, is there a way to disable the password change for the built in administrator user, via command line or registry?

Try3 said:

You cannot stop an Admin user changing passwords.

Denis