Process Folders' Custom-Field (and metadata) assignments: 

When form submitted, copy checked items to hidden field. 

Form processor:

• If break inheritance checked, and any items in hidden field, send contents to db.
• If break inheritance checked, and hidden field empty, create dummy assignment fieldID = -1.
• If break inheritance NOT checked, remove all assignments for this folder.

This method can be accessed through the CustomFields.asmx file located in:

~/Workarea/webservices/WebServiceAPI/CustomFields.asmx

[SoapHeader("AuthHeader")]
[SoapHeader("RequestInfoHeader")]
[WebMethod(MessageName = "ProcessCustomFields", Description = "")]
public object ProcessCustomFields(long folderID);

<SoapHeader("AuthHeader")>
<SoapHeader("RequestInfoHeader")>
<WebMethod(MessageName = "ProcessCustomFields", Description = "")>
Public Function ProcessCustomFields(folderID As long) As object