I've created an organization with Google Cloud Identity for our company domain. I verified our domain and added a bunch of emails that already had Google accounts associated with them. For one of the email accounts I chose not to transfer it to the organization.
As expected, when we logged in with that account we had to choose to log in with the personal account or with the workspace account.
After some deliberation we decided we wanted to transfer the account anyway, and we want the new account in the organization to have the same Google Id as the original account, just as if we had chosen to transfer the account when we first added the email to the organization.
The account isn't shown in the transfer tool for unmanaged users since it now is a temp account (@gtempaccount.com)
According to this link https://cloud.google.com/architecture/identity/evicting-consumer-accounts#process the temp account can be renamed back to an unmanaged consumer account if we delete the account in Google Workspace Admin. I did that, but the only difference is that, when logging into the account, there's no longer the choice between the personal account and the organization account. When logging in, there's still the choice of moving the account to Gmail, or to another personal email or postponing the choice, which we pick. I can't find any choice to "Rename back to corporate address" as the flow chart suggests, neither when logging in or when being logged in.
I've tried several times by recreating the organization account and removing it again, with the same result every time.