Tweets can be deleted via the remove button…but many people wish they could edit them, not just delete and repost.
A true “change what you have already posted” feature wouldn’t work, because the Twitter.com retweet link shares exact copies of your tweet. So if there was an edit button, you could change what people retweeted any way you wanted…which might not make the people you retweeted too happy.
For example, you could say “Vote for candidate #1″ and after it had been retweeted, you could change it to say “Vote for candidate #2.” Sure, they could make the edit button good only for a few seconds, but it would wouldn’t eliminate the problem, it would just make it smaller.
Twitter could implement a “delay before posting” button, kind of like Facebook and Gmail’s feature, where you have a few seconds to correct your tweet before it gets sent. That…would be terrific! What do you think?