XL Reporter: is it possible to add a user-defined Dimension?

I've viewed the documents and have not found a topic about user defined metadata. Is it possible to change the underlying definition and add a new dimension for the composer to use? For example, my itemcode is composed of 3 segments, AAA.BB.001, where AAA stands for the main category of products, and BB stands for the sub category. When making a sales report of products, I'd like to take AAA, BB as 2 dimensions respectively.

I know that itemcode can be used as a dimension, but i wonder if i can split itemcode into 2 dimensions. If not, how can I achieve this? Split the itemcode in master data using UDF?