Yes, you can install the lag-fix after CWM.
However, the lag-fix is easily the #1 reason people have blown up their phones.
If you really need the lag-fix, go ahead. Just make sure you know how to uninstall it.
I don't use it.. From what I know, Cory doesn't use it.. None of the other dev's I work with use it. For 95% of the people, this "fix" isn't going to do much, if anything.. If you're the 5% that needs it, then you need to know what it does, how it works, and how to remove it. Otherwise it's going to cause you nothing but problems.