If you make those changes to a B harp (and oddly enough I have done just that recently), you will have what Lee Oskar would call an F# minor harp. I don't know how Hohner names their minor harps, but Lee Oskar identifies them for 2nd position playing.
I also don't know how Hohner tunes their NM harps. So my apologies for not being able to tell you that.
I do know that Pat Missin has provided charts for how to tune chords for just intonation. They can be found in a file called JICHORDS.txt included in his Altered States collection of files on harmonica tuning which you can find here: http://www.patmissin.com/tunings/tunings.html
I think you need also to consider how you intend to use the harp. If you are going to play lots of chords, you might want it tuned up for just intonation which will give you rich chords. If you will be playing mostly melodically, you might want to make it equal temperament. I'm pretty sure that LO minor-keyed harps are tuned for equal temperament.
Here's a nice use of a LO F#m harp, by Bad News Brown: http://www.youtube.com/watch?v=Qp_RklNtFeg
Hope this helps (at least a bit),
John
I've got a Special 20 in B and I want to retune it to B Natural Minor
I know which notes I need to change (Blow 2, 5 and 8 and Draw 3 and 7 all need to be a half step lower), but I'm not up on the intricacies of Equal Temperament, Just Intonation, or Compromise Tuning. I want to tune it like a regular Natural Minor SP20 would be when it came out of the Hohner factory
Does anyone know where there is a summary or diagram showing how many cents sharp or flat each note needs to be in a natural minor harp?
Cheers
Mike