No, altering a garment could mean simply altering a certain part of the garment to achieve the desired fit, whereas resizing would mean changing the entire sizing of the garment throughout, this is also possible in certain cases, depending on whether or not the garment has enough inlay fabric left in by the manufacturers for the amount the client wishes to achieve if letting out. If taking in it usually depends on whether or not the balance of the garment allows for taking into too much of an extreme.