Please consider building and manipulating the entire data structure in an array step by step, it makes it easier because you can see what you are doing with pp().

use feature ":5.14";
use warnings FATAL => qw(all);
use strict;
use Data::Dump qw(dump pp);
use Text::CSV_XS;

# So original data look something like:

my @d = split /\n/, <<'END';
1,6064.86,85391.25,593.75,13.25
2,6072.17,85392.95,593.79,13.29
3,6078.94,85393.05,593.76,13.26
4,6085.51,85392.22,593.77,13.27
END

# I need to insert two lines at the top, two lines at the
# bottom, switch columns 2 and 3 around and replace column 5 with colu
+mn
# 1.I'm using Text::CSV for parsing and also Lava GUI package. So part
+ of
# the code that does parsing looks like this:D

my ($t, @t) = (Text::CSV_XS->new);

$t->parse($_) && push(@t, [($t->fields())[4,2,1,3,0]]) or die "Could n
+ot parse: $_" for @d; # Parse and rearrange

unshift @t, ["Top line 1"], ["Top line 2"]; # Top lines
push    @t, ["Bot line 1"], ["Bot line 2"]; # Bottom lines

$t->combine(@$_) && ($_ = $t->string)  or die "Cannot combine: ".dump(
+$_) for @t; # Combine

pp(\@t); # Print result
[download]

Produces

[
  "\"Top line 1\"",
  "\"Top line 2\"",
  "13.25,85391.25,6064.86,593.75,1",
  "13.29,85392.95,6072.17,593.79,2",
  "13.26,85393.05,6078.94,593.76,3",
  "13.27,85392.22,6085.51,593.77,4",
  "\"Bot line 1\"",
  "\"Bot line 2\"",
]
[download]