If the database principal was related to a login that is a windows user, there is no need to "fix" them. The function of sp_change_user_login is to align users to logins where the SID will never, ever match. If you add the windows user or group to SQL Server as a login, there is no need to do anything more since the SID from AD/Windows will be the correct SID and you are done - not need to fix anything with sp_change_user_login. Remember - AD/windows assigns the SID to the user and SQL simply uses that SID.

For SQL Server logins, the SIDs are assigned by SQL Server and issuing the same sp_addlogin/CREATE LOGIN command on different instances of SQL Server will result in a different SID (assuming that you do not specify value for the SID). This is why sp_change_user_login exists.