sub whatever {
  my $array_ref = shift;
  my @copy = ( @$array_ref );
  @copy[1] = 'whatever';
}

sub blah {
  my $array_ref = shift;
  local $array_ref->[0] = 'blah';
}

sub test {
  my @array = @_;
  $array[2] = 'test';
}
my $test = [ qw( 0 1 2 3 4 5 ) ];
whatever($test);
blah($test);
test($test);

use Data::Dumper;
print Dumper $test;