[KiLLeR.]

#define g_flLifeTime EV_FL_fuser1

entity_set_float(entity, g_flLifeTime, 100.0);

- or -

#define g_flLifeTime EV_FL_fuser1
#define SetEntFloatVal(%0, %1, %2), entity_set_float(%0, %1, %2)

SetEntFloatVal(entity, g_flLifeTime, 100.0);