There is a workflow solution to this. While you're making a model, if you think that you may want to change one or more parts of the model, make that set of parts separate bits of the mesh. This can be achieved with a vertex group, or just by leaving the part of the mesh unconnected to the rest of the object.
When you decide to select on part, select it by using the defined vertex group, or if you've left it unconnected to the rest of the mesh, by selecting a point on the part and pressing CTRL - L, or by pressing CTRL [numpad] + until the part is selected. Get the necessary parameters of the part (especially the median point location), or create the new one, if not at the desired location, in a way that you can move it there, and when it is in the desired place delete the original.