Twitter – pause/play “auto-fetch” option for Twitter

Most modern clients should support multiple accounts. I can recommend Tweetdeck It supports multiple accounts.

Twitter won't redirect tweets to your new handle if someone tweets to your old handle. Your old handle will be left for grabs so anyone will be able to use it.

I suggest you take possession of your old handle (simply sign up as a new user with a different email address) and note in the description what your new handle is (and why).

That way, even if someone mistakenly uses your old handle (which is unlikely) you'll be notified of it since you'll be in control of it and you'll be able to answer with your new handle then.

Also, if you forget you've left a link to your old Twitter handle somewhere on the web, people will still be able to find you.