[dba-Tech] Word Question: How to Swtich Templates?

Given document A, based on Normal.dot, which I have now customized for this particular document, and don't want to overwrite the old normal.dot: I copied the old Normal.dot to a new name, on the suspicion that Word would overwrite it with this version. Then I plan to rename normal.dot and restore the old version.

That said, how do I then switch the template that this document uses? 

TIA,
Arthur