This seems to do what I think you want using your data.

use strict;
use warnings;

my @strings = (
   q{asdfgGOATaewrjgn},
   q{ererGOAskjgbrTslkgjnjng},
   q{ccG<!-- comment on status of global geopolitical economics -->OAj
+gTsvs},
   q{aGO<h3>i hate clowns</h3>ATbbb});

my $needle    = q{GOAT};
my @parts     = split m{}, $needle;
my $notNeedle = qq{[^$needle]*};

my $haystackPatt = q{(} . join($notNeedle, @parts) . q{)};
my $rxHaystack   = qr{$haystackPatt};

my $stuff1 = q{^^^};
my $stuff2 = q{+++};

foreach my $string ( @strings )
{
    print qq{$string\n};
    $string =~ s{$rxHaystack}{$stuff1$1$stuff2};
    print qq{$string\n\n};
}
[download]

It produced this output.

asdfgGOATaewrjgn
asdfg^^^GOAT+++aewrjgn

ererGOAskjgbrTslkgjnjng
erer^^^GOAskjgbrT+++slkgjnjng

ccG<!-- comment on status of global geopolitical economics -->OAjgTsvs
cc^^^G<!-- comment on status of global geopolitical economics -->OAjgT
++++svs

aGO<h3>i hate clowns</h3>ATbbb
a^^^GO<h3>i hate clowns</h3>AT+++bbb
[download]

I hope this is useful.

Cheers,

JohnGG

Update: Fixed typos

Update 2: Changed initialisation of $notNeedle so string was not hard coded, original line was my $notNeedle = q{[^GOAT]*};