In a much more likely situation, they would put some kind of banner on Google.com expressing their distaste for SOPA. The same for other big companies like Facebook. I thought what Tumblr did was cool, they managed to get many people calling their local reps.
Also, I think we're concentrating too much on the big companies (not that it's really a bad thing). The little ones matter, too. Marshaling them would be somewhat easier due to their lack of hierarchical politics to make every decision.
Although you do have the problem of the multitude of people who just access the internet via Facebook's walled garden. They also have no idea what SOPA is/means.
So, if we can get the giants of the internet to do something - that's fantastic, but we need to get the smaller blogs/websites on board too.
That wouldn't be the same sort of technical challenge as SOPA would pose, but would drive home the point pretty well.
But perhaps more interestingly: because people would still have a job to do, they'd use Bing or something else, which would hopefully demonstrate to Washington just how circumventable the legislation is.
Changing the algorithm is more insidious, unless or even if you had a disclaimer on top saying you modified the result to fit your agenda. I think this is comparable to modifying the Wikipedia SOPA article to be non-neutral, which is a terrible idea of course.
In the same vein, I don't think blanking Wikipedia can violate NPOV (in its Wikipedia sense), since this policy refers to editorial content: the articles themselves need to be neutral. The concept of NPOV is simply not applicable to the Wikipedia enterprise as a whole.