Technically you can be anywhere backstage as long as you have your ID. However, if your going to the parks its easier to just go through the main entrance. HOWEVER, at MK if you are taking the CP bus back to your apartment you would want to take the tunnels and take the tunnels bus to the CP bus stop. It would be faster than taking ferry or monorail > walking to the opposite side of the ticket and transportation center > waiting on a CP bus > going to pick up the rest of the CPs at the CP bus stop > then finally start to head home
Source: I worked in transportation.