For posterity, here's how to do it:
Obtain Adobe's AFDKO font tools and install them.
Put the OTF files into an empty directory.
Run
ttx *.otf
to convert the OTF files to TTX (XML).Edit each TTX file in a text editor:
In the
cmap
section, change occurrences ofhyphen
tominus
. This table maps characters to glyphs. Character U+002D was originally mapped to the hyphen glyph; this change maps it to the minus glyph.Over the whole file, change ocurrences of
NittiBasic
toNittiBasicM
andNitti Basic
toNitti Basic M
. This will distinguish the modified version of the font from the original once it's installed.
Rename the TTX files, replacing
Nitti Basic
withNitti Basic M
.Run
ttx -b *.ttx
to convert the TTX files back to OTF.Finally, install the newly-created OTF files.