Xenofex2, Thanks for the flattering comment!
There is a very simple solution to your question. Open my template in the program and add the required number of blank slides, they will be created behind my template, then drag the left mouse button as long as you need in front of the template, and the rest will remain behind the template. Just in case, save the template under a new name and continue editing until completion.
If you have any questions, ask, if I know how to solve the problem, I will definitely inform you.
P.S. The soundtrack will need to be moved in timeline mode to the beginning of the first slide.