Is it legal to change job title on a Check stub to a position I've Never been in but require me to do the old positions requirements as well?

No, it is generally not legal to change your job title on a pay stub to a position you have never held, as this can be considered fraudulent misrepresentation. Employers are required to accurately reflect an employee's title and job responsibilities on pay documents. If you are being asked to perform the duties of a previous position without being officially assigned that title, it may be worth discussing with your employer or seeking legal advice to address the issue.