How to change the Busselector block default parameters using m-script? (Changing the default parameter value of a built-in block is not allowed)

 new_system('testModel');
 x = 30;
 y = 30;
 w = 30;
 pos = [x y+h/4 x+w y+h*.75];
 add_block('built-in/Inport',[sys '/In1'],'Position',pos);
 pos1 = [(x+offset) y (x+offset)+w y+h];
 add_block('built-in/BusCreator',[sys '/Busselector'],'Position',pos1);
 set_param('built-in/BusCreator','Inputs',15)

Now it say's: Changing the default parameter value of a built-in block is not allowed