I haven't worked in RB myself but I guess it doesn't differ much from the other companies. You can definitely influence your staffing by expressing your preference in a specific sector to the partners or principals of that particular practice area and doing the same with the staffing department of your office.
Having said that, eventually, if the office is fully booked and they need a consultant in a practice that is not your favorite one, you will be staffed anyway. This is particularly true at the beginning of your career when you have not created deep vertical know-how yet in any sector nor you have created a solid affiliation with partner and principals of any practice.