How do Twitter apps handle username changes?
My answer to How do Twitter apps handle username changes? on Quora
Twitter assigns each user a unique numeric ID which does NOT change when the user’s Twitter name changes, so triic number one is to key off that, not the username itself.
Lanyrd checks if your username has changed whenever you sign in—if it has, Lanyrd updates your Twitter name in the database.
Unfortunately it’s not possible to redirect your old Lanyrd profile page to your new one, since it can’t be guaranteed that some other person hasn’t claimed your old name on Twitter. This is a right nuisance.
For a couple of months after we launched we had a bug where changing your name would result in two entries in our database table (thankfully we could manually fix this when it happened). It took me a while to realise this was due to changing usernames.