I don't have any working cod, but I ran the following script and had problems. Every map document in the folder reverted back to 8 1/2 x 11 inch page sizes targeted to my default printer. I lost all my large-format printer settings and had to reposition and resize every element in the layout view, causing me to redo hours of work done over the last few days. Yes, I should have tried with only one map document as a test, but it's a hard less to relearn.
import os import os.path import arcpy.mapping mapFolder = os.curdir for mapDoc in os.listdir(mapFolder): if os.path.splitext(mapDoc)[1] == '.mxd': mapPath = os.path.join(mapFolder, mapDoc) print 'Regenerating thumbnail for ' + mapPath + '...' mxd = arcpy.mapping.MapDocument(mapPath) mxd.deleteThumbnail() mxd.makeThumbnail() mxd.save() del mxd