Eh... what do you mean it won't let you open Ren'Py? Hmm, you don't need to actually open Ren'Py if you're going the drag and drop trick. :)
2 ways:
- Install Ren'Py, make an alias on the desktop, and drag the whole game folder there. (This is the one that I personally do. This is also the easier one.)
- Install Ren'Py, open the application, open "preferences" at the lower right corner, then for "projects directory" select the folder where you have the game that you want to open. You can then click "Launch Project". (I can't do this one because I have a separate folder for my own created games that I use as my "projects directory". But when all else fails, I do employ this 'trick'.)
Sorry if I can't provide any other solution! As I said, I too have a mac with the newest update, Sierra, and these two solutions work perfectly fine for me. Even I still don't understand why I'm unable to open some Ren'Py games after the update, though.