validate the changes in the process data of a project area

I have a requirement in which i need to validate the changes to the the process data. Specifically we have a pre condition on the work item and we do not want this to be removed once enabled.
The best way to do so I thought was create a advisor to the Project Area Save operation.
The problem with this approach is to get the changed process data.

The operation data for the Project area save is null and most of the variables using which the modification can be fetched is private. Specifically the fPreviousItems in Project Area Save Operation.,
The below code gives me the specification as IContent.

Map data = modifiedProjectArea.getProcessData();
IContent specification = (IContent) data.get(ProcessContentKeys.PROCESS_SPECIFICATION_KEY);

But i cannot get the Process data as a string as I need content service to fetch the content from the IContent.
The fProcessService is protected which is the closest variable to get any service.

Can you please help me in writing the advisor for the project area save operation to validate the changes in the Process data.

Thanks
Aradhya