c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my @ra = (
   { 'day' => 1, 'Balance' => '183.57', 'payment' => 0, 'Total' => 0, },
   { 'day' => 4, 'Balance' => '12.86',  'payment' => 0, 'Total' => 0, },
   );
 dd \@ra;
 ;;
 my @add_after_first =
   map { { 'day' => $_, qw(Balance -  payment -  Total -) } } 2, 3;
 ;;
 splice @ra, 1, 0, @add_after_first;
 dd \@ra;
"
[
  { Balance => "183.57", Total => 0, day => 1, payment => 0 },
  { Balance => "12.86", Total => 0, day => 4, payment => 0 },
]

[
  { Balance => "183.57", Total => 0, day => 1, payment => 0 },
  { Balance => "-", Total => "-", day => 2, payment => "-" },
  { Balance => "-", Total => "-", day => 3, payment => "-" },
  { Balance => "12.86", Total => 0, day => 4, payment => 0 },
]