Is it permissible to utilize sick leave without being ill or to leave work early if the company retroactively cancels deserved overtime pay?

For sick leave to be warranted, a real illness must exist. The employee is obligated to be present during official working hours, even if there is no work available, unless permitted to leave by an authorized person. If the employer has canceled overtime hours that you worked without compensating you for them, then you are permitted to take your right in a manner consistent with the issue of al-Zafar (taking one's right by force or stratagem). If you are unable to obtain your right by any means, and you wish to compensate for it through sick leave or early departure, then it appears there is no harm in that, and it falls under the issue of al-Zafar.