You could create an SCCM job to run the net user command on every machine, but a more reliable and easier way is to use Group Policy Preferences. Makes it really easy and can be basically guarenteed to work.
strComputer = "."
strAdminUsername = "<insert admin account name here>"
Set objUser = GetObject("WinNT://" & strComputer & "/" & strAdminUsername)
objUser.SetPassword "<insert password here>"