You cannot resize if the settlement is under siege.
There are no refunds for downsizing. Premium time is not required to re-size a settlement.
''There's some confusion on this "Extend over a house" rule / ability. It does happen, but may be a bug. Once the situation is clarified, we'll update this section.''<br />
You may move your perimeter over a house you don't have the writ to. Although once you do normal rules apply and you'll need the writ to do any further adjustments.