Adding property lists for Matrix Items

Hi,

I'm new to NetSuite and we are just starting off.  I have read some posts that you cannot change an imported item into a matrix item so we plan to add our products manually.  Our products are T-shirts, so we need to add sizes and colors. 

Is it possible to add the property lists for the matrix items before we start adding the products?  I have done a couple of test products and added the property list through the matrix assistant but i would like to do a list of colors for each manufacturer before i start adding products.