I figured out the answer to my question in this thread. To change a graph title with VBA you put the following code in PageHeaderSection_Format or PageHeaderSection_Print event. Maybe other events too but I didn't pursue it that far - just know it won't work in open event, etc.
Me.MyGraphName.ChartTitle.Text = "New Title"
I'm cross posting this in several other forums because I've seen this question asked many times. Even though the replies give good code they don't tell you which event to put it in.