import os
for r, d, files in os.walk('C:/Images/Thumbnails') : # put your directory here
for f in files :
if not f.endswith( '.tif') : continue # ignore non '.tif' files
new_file = f.replace('c1', 'c01').replace('c2', 'c02')
if new file != f :
os.rename( os.path.join(r,file), os.path.join(r, new_file) )