Ok, I finally find the solution.

Thanks for your feedback, indeed a solution has to be find inside modo, but things like that are moving really slowly for big software, so I did a request here first :)

Actually in modo I have a vertex map list of 82 maps, and merging all the objects into a new layer don't process anything inside this normal map list. I tried to merge
all the maps in one ... but it doesn't seems to work.

Probably a script is required (not sure if this data is exposed via scipt), I did some research on the forum, but as usuall I don't have a lot of time, I have something like 20 ships like that to build and shade in a week.

But anyway, here's how to process.

Export the in .obj (ngones), use the mergeobj editor, import in modo and just do a [polygon>align] to flip all the inverted polygon.

I didn't try that before because I remember having bad experience by flipping polygons in modo without having trouble with the vertex normal map. But at that time (is was the headphone model), I had complete flipped parts because the solid inside MoI wasn't closed, meaning that the polys and normal where flipped.

In this ship model, only some polys are flipped, so the align command work whitout having any trouble with the vertex normal.