So I think it's better to call it a day and time to thank you for your help.
Not everything has been explained.
One day I hope I shall understand why, after a short use of a macro with Word 2013, the
letter-spacing property manages later to slip into the body of my EPUB and why I get later hundreds of useless "Policepardfaut" spans in the EPUB. These two defects can easily be eradicated in the EPUB.
But there have been some insights. I realized that Word 2013 uses forcibly some template to modify some generic styles (titles, notes) though he does not modify specific user styles (nor tables).
And last, It has been confirmed that due to some surprising "idiosyncrasy", Word 2013 is unable to keep track of the relative width of images in odt files.
If somebody manages to get more information about the management of odt files with Word 2013, this is the thread. My odt and EPUB3 files which evidence the above points stay available.