Extending Validity Period In Assigned Appraisal Documents ???

Dear Experts,

Appraisal Documents is assigned to Employee via Appcreate, where we have provided some validity period and Execution period of Documents .

Now requirement is to extend END Date of Validity and execution period .

For Ex :

Start date : 01.01.2014

End Date : 31.06.2014

Now Appraisal Period is over and appraisal document is freezed .

Is there any way We can Extend that Appraisal Period from 31.06.2014 to 31.08.2014  ???

I was trying PHAP_ADMIN_PA, where we can click on CHANGE HEADER DATES and can change Dates and other fields but that is possible before Ending of Appraisal Document .

Now I am getting Error : latest appraisal date must occur after the current date .

Is this Possible to do ?

Is there any table or configuration or enhancements where we can Extend Dates of Freezed Appraisal Documents ?? 

Its a needful thing to do..

Please help me out for way forward .

Regards,

Pran