EDIT: disabling ligatures is possible through disabling Contextual Alternates (calt), neat! And it is also possible to keep them on and change only appearance of aforementioned equal sign sequences back to "normal", using ss19. Turns out all features are nicely documented at GH Wiki [1]:
calt – Contains all ligatures. Substitution for : between digits.
ss19 – Adds gaps in ≠ ≠= == ≡≡ ligatures.
