Employer changing job duties

What is the name of your state? PA
If I was hired as a Network Administrator and was working for 3 years doing network and systems admin duties can an employer just decide that one day I should also start making sales calls?
If I say no, because I'm not a sales person and have no desire to be one can they fire me?
If I do it, will it void my non compete?
What are ways to get a non compete agreement voided?
Also, can an employer just decide to change an employee from salary to hourly and then send them home when "there's no work to be done"?

Thanks

If I was hired as a Network Administrator and was working for 3 years doing network and systems admin duties can an employer just decide that one day I should also start making sales calls? Yes.

If I say no, because I'm not a sales person and have no desire to be one can they fire me? Yes.

If I do it, will it void my non compete? Only an attorney can advise you on that after having read the agreement.

What are ways to get a non compete agreement voided? Same answer as above.

Also, can an employer just decide to change an employee from salary to hourly and then send them home when "there's no work to be done"? Nope. An employer cannot switch an employee's FLSA status back and forth to avoid paying the employee his/her regular salary.