This won’t help today’s genealogists but may be useful to future researchers. The Census Bureau has published a memo in the Federal Register that outlines residence criteria and residence situations that determine who should be counted and where they should be counted. Federal employees working overseas are specifically mentioned in this memo.
The memo specifically states:
Overseas military and civilian employees of the U.S. government — The 2020 Census will count military and civilian employees of the U.S. government who are temporarily deployed overseas on Census Day at their usual home address in the United States, as part of the resident population, instead of their home state of record. Military and civilian employees of the U.S. government who are stationed or assigned overseas on Census Day, as well as their dependents living with them, will continue to be counted in their home state of record for apportionment purposes only.
Overseas federal employees who are not U.S. citizens — The 2020 Census will count any non- U.S. citizens who are military or civilian employees of the U.S. government who are deployed, stationed, or assigned overseas on Census Day in the same way as U.S. citizens who are included in the federally affiliated overseas count.
This is a change since the 2010 census. You can read the full Census Bureau memo at: https://www.scribd.com/document/370985820/2020-Census-Memo-Residence-Criteria-and-Residence-Situations
The memo seems to contradict various rumors and speculations regarding whether the 2020 U.S. census will be conducted at all, even though it is required by the U.S. Constitution. See http://bit.ly/2FYKLRc and a number of other online services with stories about the funding and organizational problems of the next scheduled census.