#!/usr/local/bin/perl
$text = "Paulson and Federal Reserve Chairman Ben S. Bernanke proposed the plan after the collapse";
$text =~ s/\b[^<]S\.[^=]\b/\<S\.=initial\>/g;
print "$text\n";

##</code><code>##

Paulson and Federal Reserve Chairman Ben<S.=initial>Bernanke proposed the plan after the collapse 

##</code><code>##

Paulson and Federal Reserve Chairman Ben <S.=initial> Bernanke proposed the plan after the collapse