PowerPoint has a useful feature called Set AutoShape Defaults. If you want all of the AutoShapes in a presentation to have the same style – for example, a blue body and a thick red border – then you can create any AutoShape, set it to have this style, and then select Set AutoShape Defaults from the right-click menu. After this point, any new shapes you create will have the same style.
However, there doesn’t seem to be any easy way to reset the style used for AutoShapes to the factory defaults. If you want to make sure that a group of users are all starting from the same point (for example, when running a training course) there is no menu option* that you can get them to select. Sure, you could create a macro to do this, but given how easy it is for users to select this command by accident, I would expect for there to be another menu option to reset the style.
*Unless you know of something that I’ve missed. Either way, I certainly couldn’t find it myself in the options or by searching the online help.