[roger64]

Here is it. I do not have anything more than these lines. I wish I had.

#!/usr/bin/python

import sys, re

conv=2.37106301584
unit=re.compile('([^\d.]+:\s*)([\d.]+)(cm)?(;\s*)')
with open(sys.argv[1],'r') as f, open(sys.argv[2],'w') as g :
   for lig in f :
      k=unit.search(lig)
      if k :
         unite=k.group(3)
         if unite=='cm' :
            val="%.2f"%(conv*float(k.group(2)))
            unite='em'
            lig=k.group(1)+val+unite+k.group(4)
      g.write(lig)

I also had a script that had been given to me by Jellby to insert directly a file in META-INF without opening the EPUB. I thought that a similar process could be used here.

for i in *.epub; do zip "$i" META-INF/com.apple.ibooks.display-options.xml; done