TECHNICAL RESIGNATION

I am presently working as Sr. Accountant in Postal Accounts Office under Basic 35400/- I have passed SSC CGL Examination 2015 and at the time of filling up of form i intimated my office(forwarding of application does not arise as i don't claim age relaxation) but no reply received. After passing the preli & mains exam i had to submit NOC at the time of document verification. On applying for the same office asked for an undertaking 'if i passed i will not claim technical resignation'. On giving of that undertaking i was given noc. Now i am selected as Tax Assistant in CBEC basic pay 25500/- . So at the present scenario can I claim technical resignation as I intimated my office before taking the exam and in case my office denies to give me technical resignation can I file a case in CAT? Will it prove to be fruitful for me?