Zoho data manipulation

Zoho data manipulation

We have been a paying customer of zoho for over a year. Our leads database has grown to approx. 50,000 over the years. We are running into a few major issues with trying to manipulate our data in the leads module. Unless we are really missing something, we can not find a basic solution to reimport updated leads. Our old crm system was capable of doing this with no problem. Here is our situation:

We sponsor a few associations and at the end of the year they provide us with a updated lists of their members.  In past  we were able to take that list, have our crm search for the same First and Last name and then overwrite any updated data. Would take 2-3 minutes. But after a few multiple conversations with zoho on the phone as well as email support, apparently there in no simple way of doing this. The only overwrite map field available is the "email field" Well 95% of our leads dont have an email address. Which defeats the purpose.

Is it possible to change that "email" dependency field to like a Lead ID field. We really need to find a solution soon or we will be forced to look elsewhere for a crm. Thanks.