Switch Twitter Accounts in Safari?
There is no add-ons on Safari who is doing that.

Chrome : 
https://chrome.google.com/webstore/detail/swap-my-cookies/dffhipnliikkblkhpjapbecpmoilcama

Mozilla :
https://addons.mozilla.org/fr/firefox/addon/cookieswap/

By the way, I think you have to post your wish here : https://www.reddit.com/r/SomebodyMakeThis/