i have all tracks i use with real split sector.
1) open cmagic4
2) load a track
3) click on "edit gp4 info" button
4) click "add" button then write split1 and click ok
5) insert the value you want for first split time sector
6) re-click "add" and write split2 and repeat precedent operation
if you want modify also the lap number of race, click on "add", write laps and click ok, then write the laps you want.
important: everytime you modify a track (for change the cameras position, for example) you lost the data