The answer is, generally yes. If the tour offers multiple hotel categories, then it's possible (dependent on availability). Please note that not all tours offer different hotel category options.
It's also generally possible to upgrade hotels. This may not be an option for very busy times (no availability) or more rural or remote areas (when there is only one or very few options).
And lastly, this will affect the tour cost. There is no rule of thumb here and costs vary. Please inquire with a Tour Advisor for further details and be sure to let us know which tour you are interested in!