This script can automatically replase specified objects in scene (each of them) to another object. Replaceable objects should have a similar names, for example: Box001, Box002, Box003... etc.
Run script, and with button "Old" pick one of the objects, which you want to replace. Other simillar objects will be append automatically, based on their name. Then with button "New" pick an object, which will replace previously selected objects. Push a button "Run",