use Storable qw(freeze thaw);
sub rec_walk {
    my $hash = shift;
    foreach (keys %$hash) {
        if (ref $hash->{$_} eq 'CODE') {
            $hash->{$_} = freeze $hash->{$_}
        }
        elsif (ref $hash->{$_} eq 'HASH') {
            $hash->{$_} = rec_walk($hash->{$_})
        }
    }
    $hash
}

my %hash = (...);
print Dumper rec_walk(\%hash);