Here's how I would do it. There's probably a better way though :-) I'm not sure how to modify my code to use return 0, but here it is:

my $removing = 0;
while (<>) {
  if (/^MYTAG1/) { $removing = 1; }
  elsif (/^MYTAG2/) { $removing = 0; }
  print unless $removing;
}
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