Use a lookahead:
$s = 'Goldman_Sachs_2002';;
$s =~ s[_(?=.*_)][]g;;
print $s;;
GoldmanSachs_2002
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.