You *could* do it in three steps: 
my $string = "AAbfwercB(A)fjklASZaB(A)xvASABAB(A)gfdaZAA";
my @chunks = split(/B\(A\)/, $_);
$_ =~ tr/A/Z/ foreach @chunks;
$string = join 'B(A)', @chunks;

[download]
My guess is that it's a little slow, though. I'd reverse $string first, myself.

In reply to Re: look behind in REs by chromatic
in thread look behind in REs by tepas

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