The structure may not be right, but the sense is and I see your solution takes elements from my code so it wasn't all loss was it? You may find the following trivial variant more to your liking:

use strict;
use warnings;
use Data::Dump qw();
use Data::Rmap qw();

my $initial = [note => [shopping => ['item']]];

Data::Rmap::rmap_array {
    return $_ if $_->[0] ne 'shopping'; # Ignore non-shopping entries

    my @item= map {[item => $_]} qw(bread butter beans);
    $_ = ['shopping', @item];
    Data::Rmap::cut ($_);
} $initial;

print Data::Dump::dump ($initial), "\n";
[download]

prints:

[
  "note",
  [
    "shopping",
    ["item", "bread"],
    ["item", "butter"],
    ["item", "beans"],
  ],
]
[download]