Ustādh, if a person has two homes and went travelled to the other home which is in a different land, he used to think that he was allowed to combine and shorten the prayer over there, does he now have to redo those prayers after learning otherwise?

If each of the two houses is a place of residence for you, then you do not shorten or combine in either of them but only on the road between them, and this is what Imam Ibn Baz ruled; and if the second is not a place of residence and you only intended a short stay, then you are a traveller there.