#! perl
use Modern::Perl;

my $separator    = '|';
my $replacement  = ',';
my $target_count =  2;
my $line         = '1|2|3';
my $ft_count     =  0;

++$ft_count while $line =~ /\Q$separator\E/g;

if ($ft_count == $target_count)
{
    my @data = split /\Q$separator\E/, $line;
    splice(@data, $target_count - 1, 2, "$data[$target_count - 1]$replacement$data[$target_count]");
    $line = join($separator, @data);
}

print $line, "\n";