Thanks, @Francois. Your help is appreciated. If we can manage to make Brainstorm import it correctly the way it is, I think I would leave it like that for now. I can revisit BIDS compliance at a later point if it really becomes important for usability. For now, I would rather just freeze it the way it is. I already had my load of headaches with that project so I would like to be able to close it. Although there might still be improvable aspects (e.g., BID compliances), I think it is already a significant and useful improvement with respect to e.g. using fsaverage to do source reconstruction on infants.