Finaly nailed it down, with the help's of my
NDS's pointer tool & backtracer new feature (namely pointer in pointer search) :
Code:
Game Code/ID : AWDE 21C9768B
Code:
Always have the selected weapon *
620D27B4 00000000
B20D27B4 00000000
B000004C 00000000
00000670 0000000X
00000674 0000000Y
D2000000 00000000
* Change X and Y for the weapon you want (X ranges 0-3, Y ranges 0-5? Not sure of the whole values list...).
Be very careful of not using weapons outside of races (ie. in adventure mode's hub), else the game will crash (might try to add something to prevent it later).
Tested with different characters with different vehicules, on differences races. Working flawlessly.