nostr:npub1ec73me5a6pwv2lcwg6qxtugu6py6weh934w0muvngxup967x800qn3933z
Secret service for life is by statute:
https://www.archives.gov/about/laws/former-presidents.html
I didn't research whether retroactively changing this statute would violate the ex post facto prohibition, but my gut tells me that it would. It's not a criminal statute, but change the consequences for behavior.
But I didn't do the research, just going from gut.