Most existing platforms allow organizations to set their own URLs for donor portals. For example, the URL for our crowdfunding platform by RNL is https://ponyup.boisestate.edu, not boisestate.ruffalonl.com. It would provide a better branded and trustworthy donor experience if we could set our own url rather than using XXXX.blackbaudportal.com.
Yes, you create a redirect, but that doesn't change the URL that is sent from RENXT.
All references to Blackbaud and links away from the portal should be removed, too.
You should be able to create a redirect from your site to the Blackbaud portal redirect. You could redirect boisestate.ruffalonl.com to boisestate.blackbaudportal.com.