I searched SCN but did not find anything about adding new fields to ME1M output.
So now, as I found out how to do it, I want to share it here.
First you have to use users parameter ME_USE_GRID = ‘X’ to be able to change the layout of ME1M output.
Then you have to append the field to structure MEREP_OUTTAB_INFREC.
e.g. if you want to add vendors material number(EINA-IDNLF) to output, simply append a field IDNLF with type IDNLF to merep_outtab_infrec.