The "diaporama mode" is when you set the powerpoint file in projecting mode.
This is how they called it in the french version.

I have found a solution:

I have created macros that switch to the mask mode, change properties of the objet, then go back to editing slide mode. I have put button to launch macros in the toolba, therefore, even if i can launch them on the viewer mode, since I view my presentation on a second screen, all i have to do is to click on the macro buttos in editing view and it show the change on the second monitor.

It works