What is the ruling on one who answers in the negative about an action he used to do but has stopped, and his intention is for the present time, even though he has sworn to that? Is repentance sufficient for him, or is expiation obligatory?

If the intention is to particularize the general and restrict the absolute in an oath, then as long as the situation is as described, there is no expiation (kaffarah) and no sin requiring repentance, because an oath is based on theath-taker's intention. So, if he intends by his oath something that the wording can bear, his oath is directed towards that.