Dear Ariel,
Thank you so much for your very helpful answer.
We wish to use Arnopro for print. We are going to print a book which contains much Romanized Sanskrit text. Arnopro gives us the aesthetic appearance which we need, however it does not contain some of the diacritical marks for Romanized Sanskrit which we require. So, a few further questions:
1) Would there be another font which looks very similar to Arnopro or any other font you would recommend for a scholarly book and which would contain all the diacritical marks that we need for Romanized Sanskrit? These would be the following characters:
1. existing glyphs/diacritics: ñ ā ī ś ū
2. What we need: ḍ ḥ ḷ ḹ ṁ ṅ ṇ ṛ ṣ ṝ ṭ (Including capitals of course)
2) Alternatively, if we were to purchase a full license to use all 32 weights of Arnopro, would it be possible for Adobe to modify the font to add our requirements (diacritical marks)? Or, would it be possible for us to legally modify the font ourselves for print?
As Bob says, for a single purchase I doubt Adobe is going to do this for you.
Check out IndyFont, though: Indiscripts :: IndyFont | Build OpenType Fonts from within InDesign!
With IndyFont, you can create a new font just for the glyphs you need, constructing them yourselves.
So you can stick with Arno, and hvae another font that provides the necessary accented glyphs.
There may be a problem with kerning if you do it this way, though. Since these will be 2 different fonts, any kerning pairs built into Arno won't apply with your custom-made glyphs.