our $DoDebug = 1 ;

no strict 'refs';
sub dynConf{   # args are like "DoDebug" , 0
  my ($varName, $varVal) = @_;
  if ( defined ${$varName}){   # $DoDebug in symbol table
      ${$varName} = $varVal;   # DoDebug=0;
  }else{
      say "Variable $varName is not defined";
  }
}

##</code><code>##

  ...
  if ( defined $Main::VerboseLogging) {
    # some detailed logging
  }
  --or--
  if (defined BlackList::){
    # the Blacklist.pm package is loaded as well
  }