Maybe these will help you:
https://community.spiceworks.com/topic/1995291-importing-csv-with-custom-attributes
Keep in mind there are two ways to import: through the GUI or via the script that some of these posts mention.
I was actually writing a blog about this but stopped because someone at SW corrected my thought process (I had made some errors in it that needed correcting).
If you PM me, I will e-mail you a PDF of that unfinished post and comments from SW support on it.