You can re-enter the product key, and it will cause a new activation id to be generated which will work with an agent most of the time. But again, this still technically violates OEM EULA. Also know that OEM media will not accept open license keys, only OEM keys.
One other option exists as well for OEM. If you purchased your OEM version of software within the last 90 days, you can simply purchase an Open License Software Assurance (without license) which is typically around 30% of full license cost, and it will effectively convert your OEM license to a standard Open License.