You can always write

my $CRE = '0D';
my $LFE = '0A';
s{\x{$CRE}?\x{$LFE}}{\n}xms;
s{\015?\012}{\n}xms;
s{\x0D\x0A}{\n}xms;
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or

my $CRE = '\x0D';
my $LFE = '\x0A';

$_ = qq,aod \x0D\x0A another \x0D\x0A no more,;

s/$CRE?$LFE/--/msxg;
print;
__END__
aod -- another -- no more
[download]