Is it permissible for a smoker to swear by Allah to quit smoking, saying: "May the curse of Allah be upon me if I return to smoking," as a means to quit, or is this a reprehensible act?

It is not legislated to swear off smoking, nor to invoke curses upon oneself, for Allah Almighty said: (And they swear by Allah their strongest oaths that if you ordered them, they would go forth. Say, "Do not swear. [Your] obedience is a recognized obligation. Indeed, Allah is Acquainted with what you do.") This is a general principle for anyone who wishes to draw closer to Allah: let it be out of willingness, not compulsion. Even though a person's intention might be to add emphasis, this action is not legislated.