Well, the only way I know about "rotating" the sky is renaming the skya_ files... I made that when I made a sky for Belini's Abu Dhabi...
I say that because I heard about the possibility of editing the light source position, but never found out about...
However... Consider that the GP3 track is located inside a cube... The side faces are the sky + horizon, top face is the sun and bottom face is the ground...
Consider, also, that there are 45 sky_ bitmaps: 1-16 are for sky + horizon, 17-32 complete the upper side of 1-16 ones and 33-45 are the "top face" I said before...
In track editor, check the track position... Where are located the North, South and else... (of the track, most times the game track's north won't match with the real track's north, you should look Google Maps...)
The sky starts in the south... Thus, skya01.bmp is located on track's south, then it will rotate in clockwise direction... Then, it's a question of renaming the sky portion whick looks like a southern sky at that time to skya01, then 02 and so on...
BUT!!
I'm not sure if the game render the positions for itself of it's a fixed one... It's, of course, a trial-error question...
Good luck...
GPGSL-3: Fox race driver and team manager - 2011-2012 Constructor Champion - 2012 Driver Champion
Season 9 - #18 Erick Von Draxeler - #35 Marcus Bongardt