use strict;
use warnings;

open my $inFH, q{<}, \ <<__EOD__ or die qq{open: < HEREDOC:$!\n};
aaa
AAAAAA
ccc
ddd
BBBBBB
EEEEEE
zzz
xxx
yyy
FFFFFF
111
GGGGGG
222
333
CCCCCC
444
555
666
DDDDDD
777
888
999
__EOD__

my $inText = do {
   local $/;
   <$inFH>;
   };

close $inFH or die qq{close: < HEREDOC:$!\n};

my @events = (
   {  
       start => qr{(?x) GGGGGG $/ },
       stop  => qr{(?x) HHHHHH $/ },
       repl  => [ qw{ f31 f32 f33 f34 } ],
   },
   {
       start => qr{(?x) AAAAAA $/ },
       stop  => qr{(?x) BBBBBB $/ },
       repl  => [ qw{ f11 f12 f13 } ],
   },
   {  
       start => qr{(?x) EEEEEE $/ },
       stop  => qr{(?x) FFFFFF $/ },
       repl  => [ qw{ f31 f32 f33 f34 } ],
   },
   {  
       start => qr{(?x) CCCCCC $/ },
       stop  => qr{(?x) DDDDDD $/ },
       repl  => [ qw{ f21 f22 } ],
   },
   );

foreach my $rhEvent ( @events )
{
    $rhEvent->{ startPos } =
       $inText =~ $rhEvent->{ start }
       ? $+[ 0 ]
       : -1;
    $rhEvent->{ stopPos }  = 
       $inText =~ $rhEvent->{ stop }
       ? $-[ 0 ]
       : -1;
}

substr
   $inText,
   $_->{ startPos },
   $_->{ stopPos } - $_->{ startPos },
   join $/, q{}, @{ $_->{ repl } }, q{}
   for
      sort { $b->{ startPos } <=> $a->{ startPos } }
      grep { $_->{ startPos } >= 0 && $_->{ stopPos } >= 0 }
      @events;

print $inText;