generic "pattern" hahyaha

 $var =~ s{(yada)}{OtherSubstitute("$1")}ge; 
sub OtherSubstitute {
  my( $in ) = @_;
##  $in =~ s{yada}{yada}g;
  my $numlines = $in =~ tr/\n/\n/; ## count
  return "\n" x $numlines;
}
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