Tonight, I take a few hours added this feature. I understand VCASMO need such feature for a long time. Users want to edit and enhance a presentation, not just they can delete the slides in a presentation, but add new slides, replace video/music for the presentation.
Why I do not have it at the beginning, because I do not have enough deeply thinking and user experience evaluation for this feature, so I do not include it.
Now, you can try this new features in "Presentation > Edit Presentation
> Insert Extra Assets".
VCASMO, Chief Developer