In fact, this is the major difference between easyDCP KDM Generator and easyDCP KDM Generator+.

While easyDCP KDM Generator can be used to issue KDMs for DCPs created and encrypted by yourself using easyDCP Creator+, easyDCP KDM Generator+ can also be used to generate KDMs for DCP that have been created by a third party mastering station.

Just like easyDCP Player+, easyDCP KDM Generator+ also allows you to export its own public certificate. Provide this certificate containing your public key to the content owner so they can issue a Distribution KDM (DKDM) to your easyDCP KDM Generator+ installation.
You can load this DKDM into easyDCP KDM Generator+ and generate new KDMs for other recipients from it. The new KDMs time windows have to be completely covered by the DKDMs time window.