Does a supervisor on the shop floor gets any authorised letter from the management for his supervisor designation?

Is it any law, that the supervisor on the shop floor gets any authorised letter from the management for his supervisor designation?
We selected a person and given a profile as a supervisor without giving any addl. benefits and any authorised letter to him. His designation and emoluments were the same as other employees(operatives). only his job profile has been changed as supervisor.
Can we change his profile(back to machine operative) at any time after few years, since he is not got any authorised letter from the management.
If any issue will arise in future. Please give me your advice.

Dear sir,
A supervisor if is doing the same duties as operatives, he is not a supervisor. A supervisor has got the powers of supervision like recommending leave, siging gatepasses or supervision over men. What is the nature of work that your supervisor is doing ? If he is doing supervision over men and then you revert him to an operative, it will demote him.

Dear sir
If you want him to give better output, it is better to issue him a letter designating him or promoting him as a supervisor and keep a written record of the work he is doing.