As far as I know, you can do pretty much anything you want within a dream. It gets tricky when you try to use your dream body in ways that your waking body wouldn't be able to manage though.(Like turning into a piano) I remember transforming into a wolf once. When I looked at myself I was a wolf, and when I ran I had it's speed and point of view, but it still felt like I was a hunched over human being pretending to be a wolf.

It helps me to come up with rules for my dream worlds, like "I can set that building on fire, but only if I wave my hand like this." So that it feels more 'real'.

Most of the answers to these questions will vary from person to person I think. A few, like the question of sharing a dream, is already a widely debated subject in the scientific community. You'll just have to try them out for yourself. I wouldn't try studying for your exams while dreaming though, just in case.

Heres hoping I've been helpful!