Im not sure if people are still interested but as long as you flag the sections you change and make sure it has smart rendering enablked it will only repack the movie and only encode the changed sections. I think some people here are making assumptions about what it does and doesnt do. Secondly you can only compress a file so much that regardless of how much rendring takes place there is only so m8uch compression that will take place thus not degrading anything.

Cheers!