All fiends are doing force damage since Mordenkainens. Happy to drop some cold damage. rejigged stats as suggested. Leaving regen and lower hp. makes it a bit different
As you like. It's your conversion after all.
The saving throws of its Spellcasting and Vicious Mockery should be DC 22 not 21, since its Base 8 and CHA +7 and ProBonus +7.
The main problem with the CR balance is its summoning ability. If it can summon a CR 14 Ice Devil each round that counts towards Adonides's Challenge Rating, which would shoot its CR up into the stratosphere.
How about instead of summoning ice devils, it has a Legendary Ability to reposition them? Maybe it can dimension door one or more Ice Devils it can see to unoccupied spaces within X feet of Adonides. Then Adonides could have Ice Devil bodyguards escorting it and the Encounter's Challenge Level is whatever that figures out to.
Hmm… perhaps the "Devilporting" doesn't require line-of-sight and Adonides can dimension door any Ice Devil within his 120 foot telepathy range?
That would also allow the Ice Devils to be of the "Devil Summoning" variant without breaking the "can't summon other devils" rule since Adonides isn't technically summoning the Gelugon but just teleporting one who's already in the area.
Screwing people over with technicalities is the devil way!