What can I edit in a Twitter Re-Tweet?

Did, he get in jail for bad Twitter RT Etiquette?  

What's the deal with the Twitter Re-Tweet (RT)? Talking about getting more RT's seems to be all the rage lately, but what rules are their around the RT? 

What room do we have to edit a RT?  Can I merely RT the link with credit and then post my own comments around that?  Or do I need to keep the original tweet as close to the original as possible and then try to add my comments at the end if possible? Switching as many of the you's to U, and two's to 2, etc.

Shouldn't we as Twitters be able to simply RT the link and post our own comments? If we can, how would we show this? Take the below example of something I RT'd the other night.

"RT @mitchjoel: By the looks of this, Social Media is just getting started. Where do u think it's going? Add ur side here: http://is.gd/ijlm"

Can I change this to,..

"RT @mitchjoel http://is.gd/ijlm ;(The changing demo of social media and what's gonna happen next?)"

Or am I not giving the originator of the Tweet his proper credit? Or maybe, because I added new content to the tweet do I even need to give credit to the original tweeter at all for the link?

What if I read the post by Mitch, but then saw his tweet afterwards?  Do I need to RT him, or can I simply do my own Tweet?  Same question can be asked for other content on Twitter as well.  Before I post a link should I scan everyone I subscribe to in order to see if they have already Tweeted the link?

Please free me from this Twitter RT jail, and let me know what you think.