It is done like MFS returns. https://proconnect.intuit.com/community/help-articles/help/community-property-states-and-the-mfj-mfs... shows how to select whether community property state applies.

At the bottom of Screen 1, adjust the California information for RDP Filing Status

Follow the steps for MFJ split to MFS https://proconnect.intuit.com/community/help-articles/help/individual-mfj-vs-mfs-comparison/00/5547  Be very careful to mark T or S for every item so that the split is done correctly. 

Do the split after careful review https://proconnect.intuit.com/community/help-articles/help/splitting-a-married-filing-jointly-return...

The original copy will be the return that you use for CA RDP filing a joint return so remove the e-file for Federal 

The two copies will be used for federal only, so remove the e-file for CA. 

P.S. @IntuitAustin please fix the broken links in https://proconnect.intuit.com/community/help-articles/help/individual-california-information-frequen...

P.P.S Press F1 at the entry for RDP Filing Status and you should be able to get some help:

Split an RDP / MEA Joint Return?

Splitting a California Registered Domestic Partner (RDP) / New York Marriage Equality Act (MEA) Joint return is a two-part process. First, you must set up the RDP / MEA return, then you can perform the actual split. Please follow all the steps below to successfully set up and split a CA RDP / NY MEA Joint return.

Part 1: Please be sure the CA RDP / NY MEA Joint return is set up properly, as follows:

1. Open Screen 1, Client Information.

2. In the Resident Status section, select CA / NY as the Resident State.

3. In the Filing Status section, select Married Filing Joint as the Filing Status.

4. On the left-hand pane, in the Returns list, click the Add button.

5. Select California / New York from the list, and then click OK.

6. In the California / New York Information section, select Joint as the RDP / MEA Filing Status.

Part 2: After following the steps above, you are now ready to split the RDP / MEA return, like this:

1. On the Tools menu, select Split Joint Return, as follows:

1. Use the top section (CA RDP / NY MEA) for the Federal return (shown below). Check the boxes next to clients for whom you want to create separate returns, then type a client number for each new return (or accept the client numbers assigned by the program).

1. Use the bottom section (MFS) for the California / New York state return (shown below). Check the boxes next to clients for whom you want to create separate MFS returns, then type a client number for each new return (or accept the client numbers assigned by the program).

1. Click OK to save your selections.