Imported Images as Substitutions

I have imported images for the background into the same layer. However, each is a separate symbol instead of a single symbol with all the images as substitutions. My problem is simply replacing a background image in the timeline so that subsequent frames are updated. At the moment I have to drag the separate symbol into the timeline frame then drag that cell to the end of the timeline. Any easier way?

click-set in the desired timeline position
file
-import images-
select multiple images
uncheck "create symbol for imported items"

then you will have all those images in that timeline position,
now f8 create symbol, all the images are now in one symbol.

Thanks for your reply.