The census is only advisory on government expenditures. If a “Highway To Nowhere” (there are several across the USA) gets approval from Congress and the President, the highway gets built.
I would worry about a changing standard. If a conservative litigant challenges a bureaucratic rule, citing the agency’s motive, all of a sudden the liberals on the court will find that the agency’s motive is not relevant.
I have to admit that I am still not understanding what happened. President Trump wanted the citizenship question on the census forms. He was blocked and then he decided that he could get the number of citizens another way. What was the point? So he determines the number of citizens, but because of the presence of illegal aliens, the cheating States are still rewarded for cheating, and it gives them incentive to cheat some more.