That's EXACTLY what I do every year... buy the new QuickBooks Pro Desktop bundled with Enhanced Payrolland install the QB Pro software. Once that is done, I call the Intuit Payroll Service support number, have them cancel my current subscription and activate the new (bundled) one. It's a little work but it's MUCH cheaper than renewing AND I get the new version of QB. 

I actually just finished doing this about 10 minutes ago. :-)