To see this, - Open a new model - connect a Constant block to a Display block - change the final time to inf. - start the model.
Then from within MATLAB (either the command line or within a file) type >> set_param('untitled/Constant','Value','30'); and notice that the display changes. Do the same for other gain values and again see the display change.
Your model is no doubt more complex than this, but the same concept applies.