You can also return your @b array to the main like that:

use warnings;
use strict;

my @a = ("a", "b", "c");
@a = Foo(\@a);
print "$_ " foreach(@a);

sub Foo
{
  my $refA = shift;
  my @b = @$refA;
  $b[0] = "hello";
  $b[1] = "world";
  $b[2] = "Perl";
  return @b;
}
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