Alas it seems I did not understand exactly. In my code above I assume that you will open a file using open my $fh, ... and that you pass around that filehandle and not a literal string/bareword representing also a filehandle, which gets complicated, having to specify also package names. So, in the code I provided the part open $fh, '>', 'xxx'; is essential. The following works for me:

{
package main;
my $fh = undef;
VRML::printout('some lines1', $fh);
open $fh, '>', 'xxx';
VRML::printout('some lines2', $fh);
close $fh;
}

{
package VRML;
sub printout {
  my ($lines, $_fh) = @_;
  my $fh = $_fh ? $_fh : *STDOUT;
  print $fh $lines;
}
}
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bw, bliako