Is it permissible to say "May Allah have mercy on him" for a polytheist after their death?

If a disbeliever dies upon disbelief without repentance, it is not permissible to invoke Allah's mercy upon him or to supplicate for him, because he is condemned to eternal Hellfire, and supplicating for him means attempting to alter Allah's decreed and unchangeable judgment. Allah has forbidden seeking forgiveness for polytheists, and the Prophet, peace and blessings be upon him, said that whoever dies without believing in him would be among the inhabitants of the Fire. This differs from supplicating for disbelievers to be guided during their lifetime, which is permissible and was done by the Prophet.