To submit a range of items based on a single clothing mesh but with varied materials and textures, follow the steps for a basic clothing item; BUT leave "Keep Material Always" unticked.
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When you click the Prepare button you will see the materials removed.
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Submit the item and you will see an ID is assigned to the item;
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Create an empty game object in your project.
Attach the Clothing Extra Pattern component to it.
Enter the ID of the mesh object submmitted above to the Item ID field.
Drag you clothing texture into the Diffuse field and your normal map into the Normal Map field if you are using one.
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Add the virtual good script and submit.
See here for more on the virtual good script.
For multiple variations you can duplicate and modify this object in the project folder (ctrl + d).
Please note that if you duplicate a virtual good that has already been submitted and has an ID, you need to wipe the ID in the Virtual Good script and change the product name before resubmitting as a new item.