So, in a nutshell, I think an interesting experiment would be to try as hard as you can to change your belief system for a period of time.
Say you're a believer in something "more", anything really. God(s), the soul, spirituality, a bigger plan, etc... Try to live your life and think about things as if you were a complete athiest, maybe even a nihilist for the duration of your experiment. Look at people and dare to think that maybe they weren't fearfully and wonderfully made or knit together in their mother's wombs, that they aren't special. Define your own moral code if you currently subscribe to one that you didn't come up with yourself, and be 100% responsible for your own moral decisions. Think about things as if humanity is a really incredibly miraculous accident, but is not special at all (at all) in any cosmic sense (i.e. we weren't created by a God that wanted us, specificially). By extension, think about the world as if everything won't automatically be alright, as if there really isn't a big guy upstairs that loves you more than you can imagine and will make sure that you are ok. Dare to throw out your innermost securities.
Say you're the nihilist: start seeing meaning in the small things, try praying as useless as you 'know' it is. Allow yourself to get carried away by feeling of you're part of a grander picture that will eventually work out in humanity's favor. Try thinking that humans are the apple of some supernatural being's eye. Act as if every human being were inherently good, as if life truly were sacred. Go to church and enjoy singing the songs. Believe that everything will turn out alright.
These are rather extreme examples, but you get the picture. The beliefs that you alter could be anything. Say you believe in a soul, an inner essence that you want to be in tune with. Try believing that there is no self, that there is no soul, that nothing makes you infinitely special. Again, say you're the materialist. Try believing that everyone is inherently special because they have that fabled otherworldly appendage - a soul.
Say you're a diehard romantic that can quote John Donne for hours and identifies heavily with Christian from Moulin Rouge. Maybe try to identify with the Heath's Joker.
I, myself am attempting this experiment from a place of athiesm, but not total nihilism. My interest in this was piqued after I had talked with several people that said essentially, "Believe whatever helps you sleep at night". Basically, I'm wondering if that's true, if our beliefs are just something that we use to get through the day and dont really affect us on a day-to day basis.
If you didn't believe in an afterlife, if you thought that there was no such thing as heaven, would you maybe look at this world differently? Would you live your life more fully each day because you weren't 'waiting to get out of here'? Would small, discrete things change in your day-to-day life?
What i'm really curious about is how this would affect the emotional state of people. Will the nihilists become happier and the believers become sadder? Can someone change their beliefs purely on strength of will? Is the other side right? Does the other side at least have things that I can take away from it that will positively impact my life?
These are all questions I hope we can begin to think about.