use strict;
use warnings;
use 5.010;

use Readonly;
Readonly my $SPACE => q{ };

my $string = "(1,2,3) XXX (1,2,3)";
my @pieces = split $SPACE, $string;

$pieces[-1] =~ s{(\d)}{'$1'}g;

my $new_string = join $SPACE, @pieces;
say $new_string;

--output:--
(1,2,3) XXX ('1','2','3')