Yes, there is a simple GUI where you can select several different variables within the client itself. Including max block size generated, max accepted blocksize and block depth. It is able of tracking a fork and once it reaches a particular block depth it can switch over. This all depends on the settings that the user chooses. By default Bitcoin Unlimited will behave exactly like Core until the majority of the hashpower starts to mine larger blocks.
Interesting. What is preventing entities from cheating the system by running thousands of clients with bogus votes?
Essentially Bitcoin Unlimited is just giving people the freedom of choice, instead of this choice being made by any development team.
This is false. People make their choice once they decide to run Core (that's their choice; they could run other implementations).