Dallaylaen:

Yes, it certainly looks like it can be shortened. I also also played around with a prototype version so you don't have to explicitly take the reference to the hash:

#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper;

sub set_hash(+$@) {
    my $hr = shift;
    my $val = shift;
    my $last_key = pop;
    while (@_) {
        my $key = shift;
        $hr->{$key} = {} if ! exists $hr->{$key};
        $hr = $hr->{$key};
    }
    $hr->{$last_key} = $val;
}


my %h;
set_hash(%h, 42, 'a', 'b', 'c');
set_hash(%h, 69, 'x', 0, 'z');
set_hash(%h, 69, 'x', 0, 'y');
set_hash(%h, 'jock', 'shock');
set_hash(%h, 'value', 'abc', 'def', 'ghi', 'jkl', 'xyz');
print Dumper(\%h);

my $h2 = {};
set_hash($h2, 42, 'a', 'b', 'c');
set_hash($h2, 69, 'x', 0, 'z');
set_hash($h2, 69, 'x', 0, 'y');
set_hash($h2, 'jock', 'shock');
set_hash($h2, 'value', 'abc', 'def', 'ghi', 'jkl', 'xyz');
print Dumper($h2);
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Update: Repaired typo.

...roboticus

When your only tool is a hammer, all problems look like your thumb.