4. Do #3 but factor out everything but updateNode() from that code [into putVars or packVars] so it becomes

sub setVars {
    my($NODE,$vars)= @_;
    putVars($NODE,"vars",$vars);
    updateNode($NODE,-1);
}
# or
sub setVars {
    my($NODE,$vars)= @_;
    $NODE->{vars}= packVars($vars);
    updateNode($NODE,-1);
}
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Yes, I'd rather give setVars() a name that more clearly conveys that it will updateNode(), but I don't want to change every chunk of code that is already using setVars().