It is best practice to post the clip you're referring to and indicate the time around which the effect you need advice for happens.
I think you are referring to the transitions from one space to another (night hotel to day beach side for example, or car to speed boat). There is a lot of planning and a few production tricks involved. Morphing is used to create a seamless transition.
If you can be more specific in your inquiry then you can get better advice.
Yes, but it takes a lot of careful planning in production. You need to match framing, light, actor movement as much as possible when shooting the 2 scenes you want to transition between. The rest is Morphing.
Here's an older post where I describe a simple morph in AE: http://forums.creativecow.net/readpost/2/992175