Yes it will add the new tags to your contacts along with the existing tags that were already in use.
1. You can export out your data - tidy it up and then re-import with additional tag groups and it will simply merge the contacts and add the extra tags too.
Please Note: If you export out your contacts sometimes the telephone numbers/mobile numbers are affected when you come to re-import the data back in.
This is unfortunately an Excel issue so we would recommend that you only update the columns that you need to and delete the rest of the columns including Telephone, Mobile numbers etc.
2. Please make sure that you keep the ICUniqueID column and the Categories column in place on your data file as the update will match your contacts up with the IC Unique ID number inside your CRM account.
Please note: We recommend that before you do any re-importing that you take a back up copy of your contacts export and also test the re-import of data with a few sample records first.
If you have any questions or for help please contact our Support Helpdesk.