Access OpenType features of fonts?

Is there any way to access OpenType features in fonts? I’m transcribing some music that uses old Gaelic type and although there are fonts, they older style letters (e.g. ꞃ instead of a small R; ꞅ instead of a small S) have been tucked into OpenType features these days, rather than a separate font.

I tried using the LibreOffice way of adding the feature to the font name (:ss01=1), but that just stops the font being used at all.