a .w3o file is the object data file.
To get it into a new map, use the Import All Object Data option in the Object Editor of the new map, and select the .w3o file.
Anyways, I suggest just modifying it under Map Size and Camera Bounds, as Import All Object Data deletes previous data from that map, and there's not much reason to go through a lot more effort to accomplish something that you can accomplish efficiently enough anyways.