I created a title with chapters, saved it, then changed the avi file on which it was based. I would like to keep the
info in the first title, viz., chapters, but base it on the new avi file (avi flle has same name as the old file by the way). In other words, I want to open the original dmsd (dsmd?) file, but base it on the new avi file without having to recreate chapters, etc.

Is this possible?

Thanks

Not if you don't have the original AVI file!

The dsmd file is merely a set of notes as to what you want the project to look like and the files used. There is not one frame of video or image in a dsmd file.