Is it permissible to wash the hands after ablution without the intention of increasing the ablution?

This action is impermissible. It is a blameworthy form of exaggeration and an overstepping of bounds in ablution (wudu'), and it is an act that is not in accordance with the command of the Prophet, peace and blessings be upon him. This is based on his saying, peace and blessings be upon him: "Whoever performs an action that is not in accordance with our command, it is rejected." The Prophet, peace and blessings be upon him, clarified how to perform ablution, then he said: "So whoever adds to this, he has done wrong, transgressed, and oppressed."