You can localize changes to the hash...

sub my_restornator {
    local %ENV;
    %ENV = restore_env();
    
    # do things with the restored CGI object

    # goes back the way it was after this brace:
}
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If you're really clever, you could possibly make a restoredCGI object, I'm a little unsure on the details. Can it be done with Autoloader + local? Dunno for sure.