Here is my take at this but does not do it in one split and not sure if it is even possible!

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my $token  = '-----';
my $data   = "1,2,${token}0${token},4,5";
my $split  = qr/(?<=$token),(?=$token)/;
my @fields = split $split, $data;
my @newfields = ();

my $i = 0;
while ($i < @fields/2) {
    my @f1 = split /,/,$fields[$i];
    my @f2 = split /,/,$fields[$i+1];
    my @dash  = (pop(@f1), shift(@f2));
    @newfields = (@newfields, @f1,join (',',@dash),@f2);
    $i += 2;
}

my @expected = ( 1,2, "${token}0${token}", 4, 5 );

print Dumper (\@newfields);
print Dumper (\@expected);
__END__
$VAR1 = [
          '1',
          '2',
          '-----0-----',
          '4',
          '5,'
        ];
$VAR1 = [
          1,
          2,
          '-----0-----',
          4,
          5
        ];

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if you pass in my $data   = "1,2,${token},${token},4,5";

Output

$VAR1 = [
          '1',
          '2',
          '-----,-----',
          '4',
          '5'
        ];
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