This is the module in the current state.
Just goto admin/content/uc_copy_attributes, enter a node ID and select the node type to copy the attributes to.
Since the nodes will take on the type of the source node it is recommended that you edit a node in the class you want to copy the attributes to. Hopefully that makes sense. If the source node is of type product and you select t-shirt as the target class then all of your t-shirts would then be products. I actually needed this and it was the original reason for creating the module. It wasn't till I made all of the product nodes a new type that I noticed that the class attributes where associated with the individual nodes and not the class. So, just edit one of your t-shirt items and update the attributes and options the way you them to be for all of your t-shirt items. Then goto admin/content/uc_copy_attributes and enter the nid for the t-shirt you edited and select t-shirt as the target type. Bingo now all your t-shirt items have the new attributes/options.