What you are asking is what we refer to as "update on import." It is a feature we are building out and hoping to launch by the end of first quarter next year.
In the meantime, we have a couple workarounds to "bulk" update your contacts:
A. You can import a spreadsheet with all your contacts names and add a "2" at the end of their name. I recommend exporting your existing People spreadsheet and deleting all the values except the name and filling out all the new information. When you do this, make sure the email address is not the same as the old one in ProsperWorks. This is because it is the unique key we look for. But you can change all the other details, as well as adding additional emails.
Once your contacts are imported, you can sort your contacts alphabetically and merge them. All the data in each record will stay so you will have to manually go in and delete the old data. I would make two test records and try this out. We are sorry this is not the best work around.
B. The second option is to integrate with Zapier, a third party tool. It is possible to update your data in bulk using a Google sheet. If this is something you are interested in implementing yourself, I have made a handy doc to set it up! It is easy to use, and Zapier support is great: https://docs.google.com/document/d/1QPoyTldBvQIyc--T_kAS7nygcqAIvJQy2XXcPQfN8V4/edit
We also offer a paid service to help do this for you, starting at $500. Please let us know if you are interested and we can refer you to our specialist.
C. The last option is to use the API to update your records:
If you have any questions, please make a support request here