What we are expecting by importing this modified fif file (but maybe we're wrong) is to get the real baby head position in the helmet. If Brainstorm well reads the transformation matrix from the fif file during the import process to fit the head position in the MEG helmet, we hope by importing this modified fif file, that Brainstorm will display the baby head in the real position that has been included in the fif file.
We also have the coordinates of the anatomical landmarks and therefore, if it is possible to enter manually these coordinates in brainstorm, we should do it. But it is not possible (no existing tools for that) to modify these coordinates in the fif file.
Many thanks for your help François !