Is it possible to change the domain name added for the Customized Login?

Is it possible to change the domain name added for the Customized Login?

I have two domains under my "Organization". I was under the impression that I could add "Customized Login" for each domain added under my Organization. I set up one and when I went back to try to set a custom login for the other one I get a message saying "You have already configured custom login for your organization. Therefore, you will not be able to configure again." Ok, I get the message, "only one custom login for organization". So my question is, can I CHANGE the domain used for the custom login? Right now is sit/loading at "generating certificate".

Thanks!