Yes. You need to Download Magos Model Editor.(
http://www.hiveworkshop.com/forums/tools-560/war3-model-editor-62876/)
Once downloaded open the program do the following:
Windows Tab --> MPQ Browser
"MPQ Browser Window will open"
In the MPQ Browser Window, Go to File ---> War3.mpq
Units --> Human ---> Footman --> Select Footman.mdx and hit Enter
Once selected, The footman will now be in the editor.
Windows Tab ---> Texture Manager
Right Click the texture Manager and select 'Import'
Browse to the location of your downloaded texture and hit enter.
Now go to Windows Tab --> Material Manager
Double Click the second Material ( new window will open)
Double Click the second MaterialLayer
Use the drop down window and select your texture (make note of the texture's path). Hit Ok then Ok again
Double Click the 3rd Material in the list
Do the same steps as above
Close the material window. Your Footman should now have a new skin
(
Lower file size by going back to the Texture Window and Remove the Textures\Footman.blp from the List once you no longer need it.)
Go to the file Tab --> Save As "yourmodel.mdx"
Import yourmodel.mdx to your map.
Import the texture. Remove the "war3imported" from the texture path.
You now have a separate model that uses that texture, without overwriting the Footman texture.