You can change them only if the move, ability, or type change in question is in line with their pokedex entry, lore, or physiology(like a pokemon with a tail being able to use Iron Tail.

>INB4 GALE WINGS, (type)-IATE, HUGE/PURE POWER

Ex:
- Coil for the Onyx line
- Fire/Fairy Typing for Rapidash as it is a unicorn
- Tinted lens for Flygon