Importing Custom Lists

Hey all, 

I have exported my inventory list and would like to import it back in with different values for Custom List #1. 

I have manually added 5 values under Custom List #1 and thought that once I import the excel sheet it would then add all the other vaules that I have created. 

This isn't the case and it would seem I need to first manually add the values under Custom List #1 first before importing?

Thanks.