INIT_MOD(ENTITY* my_ent,par_1,par_2)
{
my = my_ent;
my.x = 200;
...
}

you = ent_create("my_model.mdl",my_pos,NULL);
INIT_MOD(you,parameter_1, parameter_2...);

or you can also directly after ent_create change parameters with you.x...