Okay. At the moment I have no GP4 stuff available, so I cannot make any screenshots and have to describe this by my memories.
#1 Starting positions:
1. To change the pole-site open the track's dat-file in the GP4-folder/circuits with GP4-builder. It might be the s1ct1.dat file.
2. Doubleclick on 'track sectors' on the left.
3.
Single-click on 'initial sector' or sector 1 (I don't remember). It might pop-up a window in the middle with some data, you can edit (Maybe it is already open right from the beginning, dunno).
4. Search in this window for 'pole-site', '1st grid position' or something like that. Make this value upsite down. For example if it is '1000' at the moment, change it to '-1000' and vice versa. In brackets behind it, the GP4-builder might tell you what this value means in metres (measured from sector center).
--> This should mirror the whole starting grid and solve you problem physically.
#2 Gridlines:
0. Make sure the folder containing your track's dat-file also contains the files named 'gridlines.tga' and gridleft.tga'. Both files are delivered together with GP4-builder-download.
1. To get also a solution for the graphical appearance of the grid lines, again open the dat-file of the track and once again doubleclick on 'track sectors'.
2. Doubleclick on the last track sector. You might see, that GP4-builder has drawn the gridlines on the sectors shown in your screen. A command list for the selected sector is shown on the left.
3. Now you have to search after the grid-lines' jip-mapping-command. For this task have a look into the jip-mapping-command, if this sector has one. Move from the last sector to the prelast sector and so on until you found the jip-mapping command for the gridlines. This command might be about 40 sectors before the finish line, but can also be anywhere else.
4. To change the site of grid lines on the track you have to edit a special value in the jip-mapping command, whose name I don't remember. In general: The GP4-bulider's guide will help you a lot with this task. Just read the chapter for jip-mapping.
I really hope, this explanation will help you.