I don't think anybody from the cast is there, from the looks of it, they are just amping up the action a bit maybe adding a couple of other Predator related items, that's why Studio ADI is there too. Could just be for some gory practical effects though.
There is only so much you can do in two days.
Also, Black has to finish the cut on August 18th and wrap the movie. That's when it will get ready for worldwide release, dubbing etc.
If they still aren't happy with the movie, the train has left the station now.