Just to make this note here so I can refer to it in the future:
Sometimes it's not desirable to allow the customer to change their own address while opening a new ticket, specially if you restricts those tickets to be opened only by authenticated users.
In this case, don' try to disable the input form since it strips out the value during the submit process. Instead, make the field readonly.
I couldn't do this on the CSS so I had to mangle the portal pages. You can see attached the like required to achieve this.
Hope it helps someone with the same need.
Thanks a lot for sharing the script,Marcos. This one's definitely going to be a great help :)
@Kalle : Re-sharing the snippet used by Marcos here.
You can paste this snippet under Portal pages -> New ticket page section.
This is amazing!!!! Thank you for sharing