If you have a 2616 and you want to make it an ACD phone, just make the changes.
"ALWAYS, when using acd and the sets associated with them, out and rebuild, you are otherwise asking for troubles~!"
That's only if they are already ACD phones and your making a change on the ACD programming, not changing a NON ACD phone to an ACD phone.
This is an Analogy so don't take it personally as some have.
Why change the engine if all you need is to change the spark plugs.