Leica will do this according to something I've read- I have a M6 classic I'm hoping will become a .85 It looks like I no longer have the pdf(?) It was from my Leica dealer I believe- and said something about the service being an enticement to M photogs to use the camera more and hopefully buy more glass. It was perhaps an extension of sorts of the ala carte program. Don't know what the cost was.
I just (last week) got a .58 M7, and it has really made using the 35mm lens so much better. Much like the 50 on a .72, as I hoped. I've gotten used to seeing so much more than the neg area.