It's important to know that if you decide to rename your subdomain (______.reportgarden.com), you are actually changing the address of your client portal. This change is immediate. Your client portal will no longer be at your old URL, and unfortunately, Reportgarden cannot set up a re-direct on your behalf. However, should you choose to rename your subdomain, all the clients should be communicated about the update as old URL no longer exists.
All the clients will now have to login to client portal through new URL. On a positive side, there is no data loss with renaming subdomain. All the clients, reports and dashboards associated with the them are automatically exist at your new URL.