Hello Sash,
Your solution is exactly what I was looking for !
I was also thinking about something with duplicating datas but could not achieve it : My brain just melted yesterday becasue I could not find how to adress all the data properly 
It was just about carefully curating the data structure !
Regardings units : it does work in my rhino files with meters as units, and tolerance at the 10th of a mm so global tolerance 0,0001 (which sounds reasonable enough for me, as even for facade I usually do not go lower than the mm)
But smart Idea to split the script between a mm and meters files with I/O-links.
Thank you very much !