You can only clear the details, you can't set them (search for "clear sso" in your product guide)
The system is set to capture the details of the windows user as you suggest, usually though it's set to only do that if the user names between windows and eepc march (again, that's in the policy in the docs)
If it was a domain account, yes, a local windows change is reflected into eepc - we don't test though with local users so the behavior is undefined. It may work, but as local changes are not reflected to network providers, I am not confident.
You have to have an ad to use eepc, so we assume you are using it on endpoints as well.