I think the only time that Google changes a word in quotes is if the spelling algorithm is very confident. For example, if you searched for [barack obama "autobiolgraphy"], you are going to get results for "autobiography" with the option to really search for "autobiolgraphy".

Other than that, I'm pretty sure that a word in "quotes" must appear in the result to be retrieved, without any alternatives. If you have a counter-example, I would love to see it! (I work on that code.)

You need to use "verbatim" mode. It's under "Search tools" and then in the dropdown starting with "All results".

This applies to the whole query, so there's not really any analogue to "foo bar +baz".

Oh so that's what this "verbatim" thing is, I'll look into it thanks.