1. Yes obviously Google does "manually" modify results. Most often, for legal reasons.

2. Manual modification isn't necessary in this scenario. Confused and frustrated people like those I describe above are likely to hit the back button, and that's a strong signal that this result wasn't what they wanted.

They do. https://www.google.com/search?q=recursion Plenty of other examples.

Adding a "Did you mean..." is not modifying search results.

Yeah, but the easter eggs have to be manually curated. - Do a barrel roll - askew - anagram ... (the list is over at en.wikipedia.org/wiki/List_of_Google_Easter_eggs)

These have to be manual. This does suggest that effects and probably the search results for specific terms can be manually modified

Could it be argued that spelling suggestions are still a search result in and of themselves?

No.

Why not? It may not be searching the web, but it certainly is still doing a search of possibly related words that you had intended to spell.

And even if it is, doesn't qualify for "manually modifies the result."

It's specific to that search term, and has absolutely nothing to do with the Google's general functionality. How is it not "manual"?

They clearly are able to create result sets crafted by their employees for specific search terms.

Google's general functionality includes suggestions. Spellcheck, even of more obscure search terms, doesn't require manual intervention. The system could easily determine that people who search for "pancales" follow up that search immediately with "pancakes".

Did you miss OP's example? Why would spellcheck give you the same word you just typed in? It's manual intervention.

They are clearly able to modify search results based on a rule system.

It's not obvious to me what the difference is between "manual" modification as opposed to "automated" modification. Surely all of them rely on looking at the search terms in an automated fashion and then deciding (or rather, weighing) what to return?

It's obvious to me. If Google changes the results of a search for "bounce" to include all the letters bouncing on the page, I can be pretty certain this was the one-time decision of a human being rather than something that was automated and, for lack of a better term, accidental.

I didn't say obvious cases are nonexistent. I merely said not all cases are obvious (and the non-obvious fraction is not negligible).

They plainly do one-off manipulations in some cases e.g. recursion.

No search results are being modified in the case you mentioned.

That depends on what you consider to be 'results'. If you consider the "Did you mean..." portion to be part of the results, then I think saying it was modified is a fair guess, since other search terms do not include themselves in the "Did you mean..." portion.