Possible to reset Keychain password without knowing the old password?
An administrator can change your login password without knowing the old password. The is no way for anyone to change a keychain password without knowing the old password.

Normally your login password is the same as the keychain password. For you to change your login password, you need to enter the old password and new password. After the software changes your login password, an attempt is made to change the keychain password. This only succeeds if the old  password you entered is the current keychain password. If not, then the current keychain password remain unchanged.

When an administrator overrides you old login password with a new password, the old password is never entered into the software. Without the old login password, the software can not change the keychain password. If you do not know the old password (i.e. the current keychain password), then you have to "Create a new login keychain". Doing so erases all the passwords stored in the keychain.

This throwing away the keychain with all the data “resets” the slate and you won’t have prompts with the new keychain that you can’t unlock since you now know the correct password to unlock.