You can edit posts before they get published. However, the duplicate content issue is pretty unclear.
There are different opinions about what exactly is duplcate and harmful. Have a look at this post and the links inside it:
http://halfagain.com/forum/rssmagician/duplicate-content-issue/msg10065/#msg10065What i know for sure is that i have 2 websites with front page almost word by word duplicate, and they both rank in first page on google for more keywords, for a pretty competitive market (over 15.000.000 results)