StellaHRA Hey snow, First thing to do is fine the original texture location in the default minecraft pack, you can download the default pack from somewhere online and have a look inside it, then find the location of say cobblestone.png which would be minecraft/textures/block - **in here*
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Then if you make your own cobblestone.png and put it in the exact same location in your itemsadder pack, and run /iazip it will update to your new version
Hope this helped.
