well.... the setobjecttexture command only works for models which have selections which you refer to... so you necessarily need to load the model in o² beforehand in order to give the models selections at all. simple objects don't have any selection.
... so you see: if you don't want to change the texture path via hex-editing or a texture swap tool, you won't be able to avoid editing in o².
and if you want to make loads of re-textured addons, i would really recommend you to get familiar with o2... believe me, it's dead simple and IMO easier than texture swap tools and hex editnig which can potentially mess up the whole model.