Import again

Hi, I did an initial import from Shopify to Woocommerce to build a beta-site. Now that my Woocommerce site is almost ready to launch how do I do to update all the information that has been gathered on Shopify up until today. Do I just do another import same as the first time? Also I have added a lot of new information (like wordpress attributes, or category attachments that werent available on shopify). Will the new import interfere with my new attributes or will the new information & products just be overwritten if I do a new import?