Amazon will blacklist the old device to disable signing into your Amazon account.
The only things you cannot do with a blacklisted device:
- Shop/download from the Kindle Store.
- Use collections.
The Fake Registration hack will enable this, but you could also manage collections using LibrarianSync or Collections Manager.
- Wikipedia lookup. Maybe any ACX (what about Bing Translate)?
This is proxied through Amazon's servers (translated from Wiki page to something the Kindle ACX can use) so there isn't a good solution or workaround -- maybe you could write your own ACX and set up an alternative endpoint.