I recently got a writers edition pen nib changed, the Saint-Exupery, for an Oblique double broad, which I believe it is the widest nib they can do on a WE pen. Once it came back the person from the local boutique explained to me that Montblanc has to fabricate a new nib for these type of requests, and in the case of Writer's editions, they only have the tools for certain years and at some point they don't keep them anymore. In these type of cases they will be able to exchange the nib for a nib of the same size (the nib if the 146) but the one used in the regular line, not with the special design engraved on the nib.
I would recommend for you to take your pen to a Montblanc boutique or authorized dealer and verify if they could use the same flour de lis nib that the Dumas has. Or decide if you are OK if they have to change it for a stock nib. @PAKMAN also has a great suggestion, a nibmeister like Mike Masuyama can help you finding tuning or adjusting the nib on your pen.
From my conversation with the rep at the Fort Worth center, they confirmed what you said. I just found out about the Dallas pen show in September so I will probably bring my pens to a nibmeister there. Do you know if the often mentioned ones will be there like Mike Bacas, Mike Mauyama, etc.?