After the Win32::SerialPort object has been created, alternate permissable baud rates can be set in the following manner:
$object->{'_L_BAUD'}{2400} = 2400;
Where the newly permissable baud rate in this example is 2400 - This behaviour is documented in the perl-win32-porters mailing list at
http://aspn.activestate.com/ASPN/Mail/Message/perl-win32-porters/2716767 where this behaviour is described with respect to the manner by which permissable baud rates are determined for a given serial device.
perl -le "print unpack'N', pack'B32', '00000000000000000000001000000000'"