Is there a way for someone to change the role they were assigned to?
I'm assuming you're talking post-arrival. It's possible - but not probable. When you accept a role offer, you commit to working in the role offered (in a location of Disney's choosing) for the duration of your program. The reason why switches aren't likely is multi-pronged.
First, the operational stability of your assigned work area depends on having a certain number of Cast Members at any one time - while it may seem like one person may not make for a big difference, you'd be surprised how much that can adversely affect an area. Likewise, recruiting & labor forecast how many each area needs and balances this during the recruiting season and prior to your arrival. It is possible that there wouldn't be another area that would be able to receive you as they'd become overstaffed.
Second, depending on your role, a significant investment is spent on your line of business and location training. For example, resort front desk hosts and hostesses (Hospitality CPs) receive over two weeks worth of training after Traditions, representative of roughly 96 hours of investment both in you, and the resources needed to train you (Disney core class facilitators and trainers).
There are more reasons, but the bottom line is that it just doesn't happen all that often. Be happy with your role before you accept it - if you're not, contact college recruiting regarding your concerns before acceptance. If the area/role you have been placed in does not seem to be a fit after working there, you'd want to speak with your leaders. After a period of time in your location, they may be able to see if there would be an area/role where you could be a better fit.
As a side note, if one were to extend their program, role switches are fairly common if desired (technically they are limited in availability) and the extension form offers a choice of roles you can be considered for in addition to your current role.