Note that the first method of LanX and Corion also works if assigning the doubled/tripled/etc. array directly back to the source array:

Win8 Strawberry 5.8.9.5 (32)  Thu 07/28/2022  5:30:16
C:\@Work\Perl\monks
>perl

use strict;
use warnings;

use Data::Dump qw(dd);

my @ra = qw(a b c d);

my $n = 3;
@ra = map { ($_) x $n } @ra;
dd \@ra;

^Z
["a", "a", "a", "b", "b", "b", "c", "c", "c", "d", "d", "d"]
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