For me there was never any need to assign the chunk border functionality to F9. It was already set up. Have you tried it already to see if it works as-is? Keep in mind that you have to press F9 twice to see the full chunk border grid. Pressing it just once only shows the boundary intersections, which can be easy to miss.
i change the key in NEI shortcut options. NEI cant be out of date if im using same modpack as Direwolf20, and i updated it few sec ago to be sure.
Could someone download Direwolf20 modpack and check if it works for him? mby DW20 on hes Lets Play had extended version of NEI
i downloaded fresh new version of modpack and it works good, problem was with my saves that were made long ago and chunk borders does not work there for some reason. So probably it cant be fixed in my old world.
I don't know if anyone is gonna read this and this is a very old post but I will post it just in case anyone has the same problem. Once you open to your minecraft directory you will see a folder named saves(as you all know this is where your worlds are saved) in that folder there is a NEI folder(If you have problems in other worlds too delete it, if not let it be) then open the world in which you have the problem(make a back up first, please I don't want to be responsible if something goes wrong) and in your world folder there is a NEI folder too, delete it and run minecraft, I am not sure if this would work but try it.