Hi! I seem to remember doing this when I used Vegas way back when, but I can't remember the procedure.
What I'm trying to do is not interpolate frames or drop frames or anything like that, but make the media go onto a timeline at a different frame rate, in a 1 to 1 frame fashion. So for example if I have a 25 FPS media, it would playback unmodifed but be very slightly longer in a 24FPS timeline.