No, it includes dialects: sociolects, slang (including technical slang), local dialects; in turn, dialects may or may not involve different accents. Switching languages is just one instance of code switching.
Not just my accent, (up and down a scale of Southern) but what vocabulary I use changes when I am talking to patients. I try to match them, so as to create a feeling of “one of us.” I have had patients who dropped out of school in the 2nd grade, patients who are actual rocket scientists, patients who have never left the county they were born in, patients who have traveled the world and everything in between. This goes for other people I meet but is particularly useful in my work.
“Does your accent change for your audience?”
All of those can involve your accent changing but none of them require it. Hence I don’t agree that code switching is what the OP was asking about. Read it again, it is purely about accent.
Yes I do that with all languages I speak.
This is almost exactly my situation (SW Va). My wife says I pick up the accent again when back home (live near DC).
I was skimming “Talking Appalachian” over the weekend and code-switching was a discussed in the academic context.
That would be really great if you would ask her about it, maybe post it to the thread for interested people?
And if her dissertation was published through a university press (as opposed to just being submitted and bound), I work in a library and can probably get it through a library loan if you don’t think she’d mind you recommending it.
I alwys thought that was a manifestation of my tendencies towards echolalia.
All this gives me hope that one day, somebody (my daughter) may give a crap that I once wrote and deposited a linguistics dissertation.
Yes, I do, especially in English and Spanish. My family constantly gives me grief about it. It’s not a concious thing, but I do sometimes catch myself. People from other parts of the country often say “You don’t sound southern!”, while people around here say I do. Even though I know only a little Spanish, people in Central and South America have told me I sound like a native.
The benefits are not insignificant - I quickly fit in to various groups because I sound like “one of them”, business associates don’t automatically know where I’m from and can’t easily stereotype me on first meeting, etc. All in all, I think I’ll keep it.
No. I speak the same regardless of my audience. I don’t have an alternate accent to switch over to.
I made a conscious choice to moderate my south Texas dialect when I was in middle school. In my twenties, I found that it would start showing up again if I was tired or had a drink in me. Later, while working tech support for beginning computer users, I learned to slip into it when I had an elderly caller, as it forced me to slow down my speech rate, lower my voice, and sound more friendly.
It still comes up when I deal with someone who’s upset, confused, or angry. While the dialect of San Antonio and south Texas is not as poorly perceived as say, southern American English, it still has some of the traits of friendliness, generosity, and openness.
Guilty! In spite of trying not to let it happen. It’s most obvious when I’m with old work buddies who made it a thing to don some persona to be especially ignorant sounding. In spite of having been one of those Gary Owens styled enunciators for a period of several years in my early days, I dropped that façade and reverted to as neutral a Southern manner of speaking as possible. But when the time is right I can put on as many voices as I can get away with. I like doing voice impressions and have been led to believe I’m good at it.
As the OP I hope I can provide some insight. First, I mentioned accent to keep the title short and that’s mostly what I do; the odd bits of vocabulary are permanent. Second, I considered discussing code-switching, but didn’t want to sound all high-falutin’. I have to dumb down my speech at work, too. 
This! My normal speech is a good 25% faster, and when I speak with many switchboard operators who are not familiar with the inner workings of the executive suite I slow it down even more. Which brings up my question for the day: Why would a company with its HQ on Park Ave in NYC hire the housekeeper from Family Guy, or a big bank in LA hire Ms Swan, as its switchboard operator? But given what I do, I suppose all I can say is, “Touche, guys. You made my life miserable right back.” 
For me, yes. I tend to bring out my Chicago accent more when speaking to others from my dialect (or for effect), and I tend to neutralize it when speaking more formally. It’s never completely neutral, but I do “clean up” some sounds.
Pure Almodovar.
Kidding. My experience with the Iberian world is so limited, I wouldn’t be able to identify (let alone imitate) regional accents within that peninsula.
I’m from southern Ontario, so I speak American Broadcast English. I also speak french, and if I’m speaking to someone from Quebec, I’ll use a Quebec accent a bit (which is the way I was taught), but with any other french speakers, I shift to a more formal France accent.
Grew up in New England with a mild-ish New England accent. 99% gone now, after living in CA most of my adult life. But when I’m back in Boston, I have to fight to not slip back into it. It’s wicked hahd, too!
When I spend time with my family, my southern accent rises again.
One our supervisors is from Boston, with a very slight accent remaining, but she can [del]camp[/del] ramp it up if I ask (it’s kinda cute). Unlike 15 years ago, few of my Boston customers has a recognizable accent, but back then our switchboard operator was told–by others–that, if the person on the phone talked funny or was unintelligible to just give them to me because they were probably mine anyway.
ETA: I never picked up that accent.
No, my accent doesn’t change. I always have the exact same accent. In fact, I can’t even imitate other accents at all. I speak French with an anglo accent, too, which I wish I could change.