You also have the right to walk off the job and seek alternative employment. Since what you're doing counts as a program change, you might even be able to do it without having your certificate be withheld. Remember, right to work is just that.
However, should you do this, you're permanently burning that bridge with that principal and district. Word will get around.
As the first responder said, call an expert in this situation, but you're likely stuck in your "new" utilization.
Also, if they're talking about cutting your stipend since you're no longer doing what you were doing before, you again have legal recourse, since you have a property right to your employment and pay level. By waiting until after the 45 day deadline to do this, you do have grounds for a grievance and for legal action - but remember, that bridge will burn brightly and hot.