After setting preferences you need to call changeText() method, like
But this is a static solution.
You could use a dinamic solution by define a proper characterStyle and take advantage of nestedGrepStyle in style applied to this part of your design.
So each character "b" could be applied with your characterStyle automatically, no need to run a script.
That's just what I was looking for. I'll let you know how it goes. Thank you.
The Paragraph Styles utility worked splendidly! I had two different sizes and styles of fonts, so I created two separate character styles and two paragraph styles and applied them to the values in place for the Data Merge, et voila! Thanks Jump_Over.