All imagery has errors. And the OSM editor have tools to align the imagery. So using GPS tracks for that area use the editor’s tool to make the alignment. Note that the errors differ in direction and magnitude over relative short distances, so just because you’ve aligned the imagery in one location it does not mean that it is aligned in another.
If there are no GPS tracks in the area to align to, then the best option is to go out with a GPS unit and create some. If that is not possible, then align the imagery to match as much of the currently mapped detail as possible so your new stuff will have the same offset/error as everything else.
I’ve looked throughout the docs and the editor interface, but I can’t seem to find out how to re-position an entire island. I’ve found out how to re-position the imagery, but the land and roads have already been drawn.