You are right, i came into to work this morning, opened up the drawing, & changed the parameter value. I also realized why i struggled yesterday. One of the values i was attempting to change was locked by relation, i just didn't notice the message warning me of this, it has been a while since i last worked with this master model & drawing. But i still stand by what is said yesterday, having 2 or more parameters in a cell seems to alter the behaviour, if you right click you don't see the 'edit value'.
John