Import ImageWriter images back in but differently

[TCmullet]

I've successfully used ImageWriter to extract individual images from a video that is largely a simple slide show. Here's a sample of my script:

frame=426
ImageWriter("slides\myProject.",frame,frame,"jpg")
frame=522
ImageWriter("slides\myProject.",frame,frame,"jpg")

It creates (in this fragment) 2 .jpg files. (in reality my script has made many dozens of individual "slides" for future use.) Now in a different script, I want to overlay the image of frame 426 over frames 20 to 30 in another video whose video clip is myClip, leaving all the other frames intact. And likewise with many other INVIDUAL images (.jpg). In fact, when I'm done, most of the original frames of the video will have been replaced by some slide from the slide collection.

I can't figure out how to do this. ImageSource appears to use as it's sole video source, the standalone images. I already have a video with audio, but want to replace a range of the video frames only (not touching the audio) with a single "slide" from one of my .jpgs. Then do this all over again for a different slide and target frame range. (Sorry if this is not as succinct as it might have been.)