It appears that after the training if employee are just refusing to accept the new type of job in the company, then it is a matter of culture of your company. They are institutionalised in their jobs and they are refusing to go elsewhere. When companies do not practice job rotation, problem of this kind arise.
You are ready to give incentive for their performance. However, have you thought from their point of view? Do they have fear that if they are placed in the job, it could take a while for them to acquire expertise and in the meanwhile they could lose their incentives in the existing jobs?
In fact you could have given little more information. What type of job training do you impart, after the training what type of job they are supposed to do, how many persons are trained etc.
When the positive discipline does not work, we need to resort to negative discipline as well. Whoever refuses to work in the job, they may be taken on task. However, this suggestion depends on the internal dynamics of the company.
9th June 2017 From India, Bangalore