The version of #5, with John's correction in #6 included, did what it should. Now my next step is to reintegrate the other paper formats via if.

I'm curious, which of the following options is going to happen:
1. Everything will work fine - that would mean, to solve the problem of overwriting a presentation with the one opened in a better way than with my workaround (FakeObject) solved all problems of my macro
2. Errors still occur - because they have to do with the change of size for 16x9
3. There is even more to fix

In case it is the third option, I will probably report ... so far: Thank you, John!

Oh, by the way: There is no easy way to include a special customized paper size in the if-options, is there?