Can the Census be altered if it's in the archives?

We don't change census records or any other records in the National Archives.  If the census indicates the wrong name, age, or anything else for a person, the mistake stays there. It's part of the record.

If you are saying there is some kind of annotation on the census record, would you please indicate the name, census year, town, county, state, and enumeration district and page numbers?  It is impossible to formulate an answer to this specific situation without seeing it.  There are many annotations on census records for the benefit of the computers (persons who operated tabulation equipment for compiling statistical data) but this does not sound like that kind of situation.

The census is as historical record (including any errors) and cannot be altered.  Some websites, such as Ancestry.com allow you to add comments or alternative names, but not change the record.