So, a couple of years ago I submitted a post asking if there was a way to change the public url of Portal. I work with many companies using ArcGIS Enterprise, and this not an uncommon need.
Of course I was informed this was not supported because Portal stores its full url deep in the bowels of its configuration. The recommendation was to "simply" rebuild the Portal from scratch.
I'm hoping Esri has finally realized that this is completely unacceptable for "Enterprise" level software. The amount of effort required to rebuild all the web maps and apps is mind-boggling.
Please, someone tell me this has been addressed in 11.x