If suing the federal government, you should be able to do this in the closest U.S. District Court to your home. It is not likely venue would be challenged.
Before proceeding, you need to understand the exact reasons why your prior avenues of appeal lacked jurisdiction to hear your case. It may well be the federal court will also lack jurisdiction for the same reasons. This would be true if you waited too long to appeal.
Beyond that federal pensions are calculated based upon grade level, years of service, and salary. If a change in job title is accompanied by a reduction in grade and/or salary, that could negatively affect pension.