debug "this..." if LVL1;
...
debug "that .." if LVL3;

##</code><code>##

sub debug {
  print "$_\n" for @_;
}

##</code><code>##

BEGIN {
 ... read the levels that should be ON to %debug 
 for (1.. $count_of_levels) {
  eval "sub LVL$_ () {$debug{$_}};";
 }
}