Hi Ron,
I don't think that you will get this to work. I suspect that when the form is reopened the Template DOM contains the original name of the text field and that this is used when the form is rendered.
You could test this with a temporary button with this is the click event:
console.println("Textfield name BEFORE remerge: " + TextField.name);
xfa.form.remerge();
console.println("Textfield name AFTER remerge: " + TextField.name);
You would click this AFTER your other script has changed the name of the text field. Also you will need to open the JavaScript Console (Control+J) in order to see the results.
Good luck,
Niall