Importing a new list into campaigns

Importing a new list into campaigns

I'm in the middle of switching my email platform to campaigns. I have a list that I want to import, and it overlaps with my existing Zoho CRM list. The fields in my Zoho CTM are more robust. 

Will this new list that I upload into my campaigns overwrite any data? My primary concern is about losing some of the work I have done in the CRM.