The simple answer is no, you cannot add a defendant to a federal lawsuit without amending the complaint.
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Defendants can be added in a civil case with leave of court. This appears to be a civil matter not a criminal matter. Consult a federal civil attorney regarding procedures.
Of course, every answer is based on the question asked and requires a more complete context. This answer should not be relied upon to make a legal decision. Seek the advice of an experienced criminal defense attorney before acting. Law Offices of Raymond G. Wigell, Ltd. Defenders of the Constitution since 1975/ Aggressive Creative Defense Strategies/ Website: www.waaltd.com 24/7 call (708) 481-4800 text (708)218-0923