So in my emerald version, I taught my Electrike hidden power, which turned out to be a fire type move with somewhere around 50-60 power I estimated. When it evolved into Manectric, hidden power turned into an ice move. Does the IV of the Pokemon change as they level up or evolve, which causes hidden power to change?
No.
IVs and therefore the type of Hidden Power will not change when a Pokémon levels up or evolves. IVs are set values a Pokémon is either hatched with or caught with
You cannot change a Pokémon's IVs once caught and there is no way to know the exact IVs in-game.
The situation that you described was most likely a misunderstanding of the original type of the Hidden Power.
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