N.Y. Comp. Codes R. & Regs. tit. 4 § 4.10
When a permanent competitive class employee is given a temporary provisional or trainee appointment or promotion to another competitive class position in the same department or agency, or is given a trainee promotion to a position in another agency, or is promoted on a temporary basis to a higher grade position in another department or agency in which he will be eligible, after six months service, for contingent permanent status as provided in section 4.11 of this Part, he shall be deemed to be on leave of absence from his permanent position for the period of his service under such temporary, provisional or trainee appointment or promotion. He shall be entitled to return to his permanent position upon the termination of such temporary, provisional or trainee service. An employee who voluntarily elects to relinquish his temporary, provisional or trainee status and return to his permanent position shall give reasonable notice thereof to the appointing officer having jurisdiction over his permanent position.
N.Y. Comp. Codes R. & Regs. Tit. 4 § 4.10