How do I set personal links so that they can be updated?

I'm not sure if it this can be accomplished using the regular features, but one "tedious" option could be to only provide them the retake URL. (read more here)
I'm thinking of something like, generate personal links. Click on them to start the survey and get the response IDs. Close these responses. Use these Response IDs to generate retake urls.
A significant portion of the process can be automated, so it may not be that tedious.

Thanks for your answer. This may work for a smaller group but I'm looking at over 1000 users. I would have to create the retake URL manually for each one.
Something I have been getting to work is going to the Distributions section, and when I compose the email to send the Personal Links, I change the Link Type to Multiple Completes. This allows the user to retake the survey using their Personal Link which does add to the reports. The only problem is that the survey will not display your previous responses so you'll need remember what you entered before.

Oh okay. I thought having multiple responses from the same individual would be a problem.
Since you are fine with multiple completes, then its really simple. Just create embedded data for each answer that you want to prepopulate and set it as the default choice.
At the end of the survey, create an action to update the contact details with these embedded variables. The first time it will be empty, and pulled from the directory the second time onwards.