As temperatures fall, it will become increasingly difficult to keep a hose from freezing which will render it useless for performing water changes. As far as being able to make changes in the cold weather, the layer of ice over the pond will allow water to be added without significant changes in the water temperature. The tap water should be warmer than the pond water but the ice will quickly absorb any additional heat.
A much better approach would be to make a lean-to over the pond using 2X4's and 6 mil poly sheeting which you can buy at Home Depot or Lowes. If one side is raised enough for you to enter, you can enjoy your fish all winter in a pond that has much warmer water than it will have without the cover. The cover allows for some build up of solar heat, reduces evaporation which is a major cause of cooling, and provides a warm air buffer between the warmer water and the cold atmosphere. In the area of the poly sheeting you can find adhesive zippers which can be placed on the poly and then the opening can be cut to allow ready access.
Zone 7 A/B
Keep your words sweet. You never know when you may have to eat them.
Richard