use Foo;

Foo->err_raise(1);
Foo->err_raise(0);

##</code><code>##

use Foo qw(:err_raise);
use Foo qw(:err_ignore);

##</code><code>##

package Foo;

use Exporter;
@ISA = qw( Exporter );
...
sub import {
   my ($self, @args) = @_;
   ...
     check @args for :err_raise, :err_ignore
     change err handling defaults
     remove those fake tags from @args and call the real import 
   ...
   $self->export_to_level(1, @cleanargs);
};