Hmm, I'd recognise the change in slang as form of code-switching, but the change in tone/accent I didn't think was part of that specifically as it's within the same language.
If using a different accent (different range of frequency, different speed, different tone) isn't changing one's voice then I'm not sure what really counts? At this point it sounds like you're trying to use a non-physics based concept for voice [the parameters of sound produced by vocalisation].
The movie "Do I Sound Gay" has an interesting take on this kind of thing. There's a stereotype of the "gay voice" (a bit higher-pitch, with sibilance on the "s"es, commonly incorrectly called a lisp). The 'intensity' of the voice-modifications depends largely on one's social environment. I don't remember the movie using the term "code-switching", but it certainly did seem like the same thing. I notice this myself - if I'm with other gay men I do usually adopt a bit of a changed speech-pattern totally unconsciously.
Speech is so nuanced; it really seems true that 80% of what you say has little to do with the words themselves.
This is known as code-switching. It's different from modifying your "voice" (although I suspect code-switching to a different pitch may kinda count).