overwrite title

I have played with overwriting text on charts by using 'white' text and 
various other tricks.
As David W. said, there's usually a slight ghost left behind.

My recommendation would be first and foremost to set up a miniscript to 
regenerate your plot, and change the title text to whatever you really 
want, rather than hacking the display via overwrites.

Second, you might want to draw a borderless box )with fill color equal 
to your chart background) over the existing text, then write the new title.

Carl