AWS SSO - User portal customize URL with external IdP (SAML)

Hello,

I enabled AWS SSO service with external identity provider (SAML) and default URL user portal (d-xxxxxxxxxx.awsapps.com/start). Everything works fine

Now I would like customize URL (ie: my-company.awsapps.com/start) and I have following doubts/questions.

After customization:

• does default URL (d-xxxxxxxxxx.awsapps.com/start) will be still active?
• does customization impact on SAML configuration at IdP side or metadata doesn't change?
• AWS doc say "This change to the user portal URL is permanent, and you will not be able to edit it later". No way to do it even involving the AWS support?

Thanks for anwser. Andrea