This can be quite complex to achieve. iRealPro uses different voicings for any particular chord type.
An option to choose between closed and open voicings would be great for a particular song.
Customized voicings is a good idea but I'm afraid it might me too complex to implement.
However, some important chord types are still missing, and I wish those would be added in the future: minor add9 without 7th (1,b3,5,9), major b5 without 7th (1,3,b5), dominant 9 without 3rd (1,5,b7,9)