Is there any way to change the shader code variable
at runtime? Here is an example :

// main.c
float myValue = 0.65; // this value may change at runtime

void main()
{
.....
.....
}

// Here is the part of the shader code copied
// from Terrain multitexture of mtlFX.c
//....
//....
// Add the vertex light and shadow map
#ifdef SHADOWMAP
//entry: Shadow Map Offset
//cntl: spin 0 1.0 0.05
//help: Light offset (0..1) to be subtracted from the shadow map

float offset = myValue;

FinalColor *= In.Color + (MaskColor.b - offset);

Thanks for any help.