Okay... This is quite rare for me to answer technical questions, but here goes!
1. You must use TrackED which is situated in the main Racer Directory.
2. Open TrackED
3. Press the 'Select Track' button and type in the name of the folder of the track. (In this case: carlswood_nt)
4. After your track is opened press the 'Declare grid pos' button and type the name of the grid position you would like to alter (the number starts from 0, so 0 is the first grid pos ect....) And if you would like to create a new grid pos leave it empty.
5. After you have chosen your grid pos, go to the place you would like to position your grid pos, press shift, and drag your mouse so that a line sort of thing appears where you want the grid to be. This should be in a straight line parallel to the track and straight. (It should appear like the other grid positions in the track).
6. When you have altered the track press -shift+s- or the 'Save track' button to save the track.
Hope I made this clear to you. If you do not understand some of it please ask!