Is it permissible to change the intention of perpetual fasting (Sawm Al-Dahr) to fasting on behalf of a deceased father?

If your father had an obligatory fast to make up and then passed away, it is recommended for you to fast on his behalf, based on the Prophet, peace and blessings be upon him, who said: "Whoever dies owing fasts, his guardian should fast on his behalf." However, if he did not owe any fasts, you may dedicate the reward of your fasts or any other act of obedience to him without changing your original intention. It is also permissible to change your intention and break a voluntary fast, unless it was a vow.