Ok, I warmed up to this solution, thanks oshalla! 
# pre build a pattern  "foo\.edu|fum\.edu"
my $what = join('|', map(quotemeta, keys %main::fixers)) ;
sub tweak_links($)
{
    my $text_ref = shift;
    return($$text_ref =~
     s!(?<="http://)($what)(?=["/])!$main::fixers{$1}!ge);
}

[download]
The overall script runtime dropped in half (0m4.8s vs. 0m7.2s on a test directory).

In reply to Re: Replace after match in regex (key value subsitution) by brycen
in thread Replace after match in regex (key value subsitution) by brycen

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