CM7 already has 802.11n support in the ROM. This fix is unnecessary for CM7 users and does not work on CM7 anyway.Is there a way to change this back and forth? I use both CM7 and Stock Sense.
If you are using the Stock sense ROM (assuming the one linked in the first post), then you need to flash the provided zip.
Once you do, you will get 802.11n support. If you switch to another ROM, you will lose this fix. If you NANDROID your stock sense ROM after applying this fix, but before flashing to CM7, then will the fix will be a part of that NANDROID and you will get it back after restoring that NANDROID.
Hope that helps clarify things.