EDIT: Disregard post. I didn't understand what was asked.

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I don't see why you need complicated algorithms here. Push will take multiple values - why not use it? See below for various methods:

use strict;
use warnings;

my %hash = (
  one => [1,2,4],
  two => [5,7,9],
);
my @new1 = (10,11,12);
my $new2 = [13,14,15];

push(@{$hash{one}}, @new1);
push(@{$hash{one}}, @$new2);
push(@{$hash{one}}, 16, 17, 18);

print join(',', @{$hash{one}});
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