I am doing exactly that right now, except my source footage was 24pAdvanced DV. I captured the footage at 29.97 and threw my clips into a 29.97 sequence and edited away. Now I have created a 23.98 sequence and copied all the edited clips from the 29.07 sequence and pasted them into new 23.98 sequence. All the clips now show they need to be rendered, but instead i am selecting each source clip and removing the advanced pull down (under the tools menu.) As I do this each edited segement from the clip changes from being needing to be rendered to NOT needing to be rendered.
I suspect it would work this easily if I just rebatched with pull down removal on.