It would be interesting to pass the projectile to the function that handles the projectile impact. Changing the flying projectile is not possible. You can access the currently flying projectiles by levels.projectiles[] (new scripting engine),
PHP Code:
TProjectile (TGraalVar):
angle - float (read only)
fromplayer - object
horiz - boolean (read only)
params - string
speed - float (read only)
x - float (read only)
y - float (read only)
z - float (read only)
zspeed - float (read only)