If it gets good enough eventually you can bet games will do this at their core too rather than re record lines whenever anything new or different is needed. Then mods just need to add the new script.

I know at least one studio that's already using AWS Polly, (IIRC) for at least prototyping voice lines. I'm not positive that they end up in production, but I've heard samples and IMO they could fly as-is for at least informational lines. I've not yet heard TTS even attempt lines with strong emotion, though.

Is it possible to create a voice changer with these kind of AI?

In principle this could be done, even with decent results.

It would basically involve a two-step approach where the first model extracts text and intonation and the second model synthesises the target voice.