Ask in the scripting forum. Someone may be able to script it.
You don't really need to duplicate or crop the image at all, I suspect. Just Scale what you have to the size you want and position across the two-page spread. If the pages are not arranged in your layout as a spread, resize the original as if they were on the first page, then copy and paste in place on the second page.
Many thanks for the responses.
Just one question to Peter Spier: I tried something along the lines of your suggestion i.e. extending the frame across the two facing pages and resizing the PDF.
However, I have margins, and the graphic currently seems to run continuously across the two margin regions - this doesn't seem to be okay for the printing later.
Is there a setting/step I missed?
Do you really want a white stripe running through the middle of your image?
many thanks for the feedback.
I guess that illustrates my specific issue - I want to *break up* the PDF over two facing pages with the margins-gap in the middle without losing any of the content - sorry, I forgot to mention there are multiple columns in the PDF content so one can do this in my case (leaving a larger column break than in the original PDF).
I will just go ahead and make the duplicate and use the frame border for cropping ...and try somehow to get an efficient workflow going.
Still, the question of whether one can independently crop the PDF for multiple instances in Indesign seems to addressed - not possible without scripting.
If you export the sample spread (which has just one image in the background, spanning the pages), you will get individual pages with the correct portions of the image on each page.