I have seen cases where people serving armed forces change their name. This is a little bit complicated process because, after changing name, the affidavit is required to be given to the Commanding Officer (CO) of the unit where the person is serving. The CO then forwards the affidavit to the higher-ups and also to the Defence Accounts (for pension and other retirement benefit purposes). It takes time.
Till now, I have not come across any case of change of name of an army pensioner. But I feel that after the change of name, the person has to forward the affidavit and advertisement to change the name to the concerned Defence Account Unit, Principal Defence Accounts Office (Pensions), Allahabad and also to the Unit from where the person retired. It would be very complicated and time-consuming. There may be a possibility of not getting the pension in time for a long period until the issue is settled.
I would advvise not to go for such a change after such a long time after retirement.
"If you are killed in action, you go to Heaven. If you win, you rule this Earth (as beautiful as Heaven). That is why, O son of Kunti, take a firm resolve and fight!"-- Shrimad Bhagwad Gita