You cant change this message size/radius.
you can make same like this message , and then change your radius/size.
example
PHP Code:
public fwd_PlayerPreThink(id)
{
static origin[3]
get_user_origin(id, origin)
message_begin(MSG_PVS, SVC_TEMPENTITY, origin)
write_byte(TE_DLIGHT);
write_coord(origin[0]) // x
write_coord(origin[1]) // y
write_coord(origin[2]) // z
write_byte(floatround(FIRE_LGHT_RADIUS2/5.0)); // radius
write_byte(255); // r
write_byte(255); // g
write_byte(255); // b
write_byte(1); // life
write_byte(1); // decay rate
message_end();
}
this what i have done for you looks same like this message "EF_BRIGHTLIGHT"
And you can change color/size now.