What do you mean?

use LWP::UserAgent;
my $aa = LWP::UserAgent->new;

my $rr = $aa->requests_redirectable;
push @$rr, 'POST';
$aa->requests_redirectable($rr);

my $ua = LWP::UserAgent->new(
 requests_redirectable =>   ['GET', 'HEAD', 'POST' ]
);

my $push = LWP::UserAgent->new;
push @{ $push->requests_redirectable }, 'POST';


print join '  ', @{ $_->requests_redirectable},"\n" for $aa, $ua, $pus
+h;
__END__
GET  HEAD  POST
GET  HEAD  POST
GET  HEAD  POST
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