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I think there are enough Voice and Vocal Tropes that you can specifically mention the new meaningful voice type instead of just the fact that it changes.
For example, in Characters.Portal, GLaDOS has two voice styles: Creepy Monotone and Softspoken Sadist. Both are listed as examples, even though the latter is only used for about 5% of the game. Both are still valid and played straight as tropes, even if in different timings or proportions.
The one I’m looking for is when a voice changes to denote taking a level of competence and maturity. The tropes in that index don’t really fit the bill.
Something like Expository Hairstyle Change , but for voices. It’s not Vocal Evolution ; this trope would be intentional rather than incidental.