Chapter Approved isn't really a matter of 'allowed' in this case... It's the newly adjusted point costs that GW expects to further improve game balance. These are final (until the next Chapter Approved or faction Codex comes along) and simply the 'current' point cost for Matched Play. These are probably the reason most people pick Chapter Approved up in the first place.
Ask not the Eldar a question, for they will give you three answers; all of which are true and horrifying to know.