Can you change your username to one that is currently in use?

No, on most platforms including Twitter, you cannot change your username to one that is currently in use by another account. This restriction exists to prevent confusion and to ensure that each username is unique within the platform. Here are the typical rules regarding username changes:

1. **Unique Username**: Each username must be unique across the platform. This means no two accounts can have the same username simultaneously.

2. **Availability Check**: When you attempt to change your username, the platform will check if the new username you want is already taken. If it is, you'll be prompted to choose a different one.

3. **No Overwriting**: You cannot claim a username that is already in use by another account, even if that account is inactive or has been suspended. Once a username is taken, it remains reserved for that account indefinitely.

4. **Impersonation Prevention**: This policy helps prevent impersonation and confusion among users. It ensures that each account can be uniquely identified by its username.

If you want to use a specific username that is currently taken, you'll need to choose a different variation or come up with a unique username that hasn't been claimed by any other account.