For the evalphobic...

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11137057
use warnings;

my $arr=[1,2,3,4,5,6,7];
my $loop="2,4..5";
splice @$arr,$_,0,999 foreach map { /\.\./ ? $` .. $' : $_ } split /,/
+, $loop;
use Data::Dump 'dd'; dd $arr;
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Outputs:

[1, 2, 999, 3, 999, 999, 4 .. 7]
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