Does rhy cause soft mutation or can it also be cymylog?
Yep, according to this BBC article, then rhy causes a soft mutation in any adjectives following it. Gymylog also feels right, in my opinion (it flows more nicely off your tongue).
Thanks! Although that implies that cymylog is incorrect, even though you answered ’yes’. Gymylog is the mutated version, not cymylog.
Ah sorry, my bad - I meant yep, it's mutated, you're right! :P