Technically after you put the texture with its path provided, the skin will replace the original texture in that map. Of course, you need to restart the world editor to see it effect or test the map instead. For example this skin with its path provided as Units\Human\Jaina\Jaina.blp.
Just change your unit or hero into Jaina model and test it out for yourself on Art - Model file in Object Editor.
Import a texture, double-click on the imported texture and replace "war3mapImported\Jaina.blp" with "Units\Human\Jaina\Jaina.blp" (without quotes), apply, save your map and open it again. Changes made will applied