Win32::OLE::Const->Load('Microsoft Office 12.0 Object Library'); I could not determine which Office to load
Yes, that's a little tricky; I actually had to check the registry at HKEY_CLASSES_ROOT\Typelib to figure that out for my machine. There's probably a way to get that information programmatically (I do see some code in Win32::OLE::Const relating to TypeLib), but unfortunately I'm not an expert on that.
So I'm going to try to extend that module to include the definitions I found in MSDN for the shapes
You can certainly try doing that, although I thought you said in the root node it didn't work when you tried your own numeric constants? If it were me, I'd first expend some energy trying to see if I can get the constants from the TypeLib before hardcoding my own constants.
I want to update the original Win32::PowerPoint module (and sub modules) back in CPAN as opposed to adding a new module cloned and forked from the original - so any pointers on how to start down that path would be very helpful.
The first step is to get in touch with the author of Win32::PowerPoint, for example by filing a pull request with your modification suggestions. If for whatever reason there is a disagreement about adding your features into the distribution, instead of forking, you can design your module as an add-on; since the module is OO, you should be able to create a subclass, and then release that as a distribution to CPAN. If for some reason the author is unresponsive, see How do I go about maintaining a module when the author is unresponsive?.