Dimensions can be over ridden in Draft, but they cannot change the model. If you need to update the model, double click on your drawing view which will open the model, make the change, and then close and return to the Draft and update the views.
You don't really even need to go to the trouble of hiding the dimension and using the prefix/suffix. You can simply click on the dimension value and change it to whatever you want it to be. This, by default, will place a line under the dimension indicating that it is no longer to scale. The "not to scale" underline can be modified or turned off completely under properties if you so desire.
That said, just because you can to do this, doesn't mean you should do it. In my group, changing a dimension like this on a production drawing rather than editing the model and making the dimension correct would constitute a hanging offense.