There is a section on Access Control and below that is for IPv4. In there it says to add a "priority" and shoes higher priority is processed first. When creating your ACL is is good practice to leave about 10 numbers between ACEs so you can insert other ACEs as needed. For example you numbering could go like this:
1
10
20
30
etc
As for the "Entry Already Exists" if that's the case and an entry for what you're trying to add does exist then it wont add the same entry twice.
