Was able to reuse HUAWEI HG633 ADSL router by simply putting new ISP broadband login information in web interface at Internet, Internet Connection, EDIT.
Internet Connection and Internet Password
Do not forget to SAVE, and reboot router.
Was able to get login info over phone by calling technical department. Am very careful not to touch RESET
Still got original ISP logo all over router. Using this forum as a way of search engines indexing this post.
Which other routers have been reused with new ISPs?