I'm basically just adding to what was in my previous post on this. Mark Krikorian has another Corner post on the Census, which has some interesting bits. His advice doesn't change though: 'Question 9 on your census form — check "Some other race" and write in "American." You're doing nothing wrong. And you may help set something right.'
Incidentally I, in contrast to Krikorian, do have a problem with the gov mailing out a letter saying that we will get a census form in the mail later. That strikes me as government waste. I suppose the theory is that an "it's coming" letter will result in more people filling out the census, but that's bollocks.