mail merge problem

i am a teacher creating tracking docs for kids as they progress through the year. The document is created by mail merging (using excel as source data) and also within the doc i mail merge pictures of projects. When the file is mail merged this creates a doc that has all the pupils identified with a picture of their project and i would comment on the project. This is the tricky part... some pictures of projects dont exist yet as the kids haven't completed the project. I can create the folders for the pictures and the mail merge link in the original merge template. i can re merge the document to update the pictures but then i would lose all the info i had typoed in the other doc?
Is there any way i can mail merge pupil names and other info and get the merged doc to update afterwards so that the pictures update to the location