Surname change post marriage

The procedure is simple and you can search website of Passport . Formats  for applying, fees and rules and regulations are uploaded in their site.  

1) Is it a law to change surname in passport as per marriage certificate or it’s just part of our Indian custom?

There is no such law that mandates the wife to change her surname post marriage also it is not mandatory to change her surname after marriage to that of her husband's surname, she can very well continue with her original surname during her entire life time.  Even Indian custom do not demand such a change.  It was just to satisfy the male egotism that the women were subjected to such changes with or without their willingness to do so.   Matter of fact the south Indian women do not adopt  their husband's surname after marriage neither they are compelled to so. 

2) If we get the change(exactly same as in marriage certificate) done in passport, then accordingly do we need to change as well her PANCARD, Bank Account details, etc or these documents can be left as it is?

Changing her name in the passport according to marriage certificate need not necessarily change the name in the PAN Card or AADHAR card or bank account.  But having two names for a single person will always complicate things, so better think what is to be done on that occasion. 

3) If she keeps her passport name as it is now even after renewal but definitely include spouse's name , then what difficulties we may encounter in future? 

She has to mention her spouse name in the passport but for that she need not change her own name, she can retain her name and can add her spouse name in the column for spouse name. There is nothing wrong in it if her surname doe snot matches with her spouse's surname. 

Hello Sir,

Thank you so much for your response!!

My wife's Educational Certificates, PASSPORT, PANCARD, Ration Card, Voter ID and Financial Documents (Bank Accounts, Fixed Deposits, PPF, Life Insurance Policies, etc) have her maiden name i.e. Amrita Ghosh (she is bengali) mentioned in them because these documents were obviously issued before marriage.

Our marriage was solemnized on Jan 2012 and registered on April 2012 in Kolkata. When we got our marriage certficate , her last name was changed to my name with a mention of her maiden name as well by using the word ‘nee’.  That is , in the certificate wife's name mentioned as Amrita Suresh nee Ghosh (since my name is Suresh Kumar Babu).

So this has created confusion for us.

1) What I understood from your response is that even if my wife's last name got changed to Amrita Suresh nee Ghosh in marriage certficate , we can retain forever her maiden name - Amrita Ghosh in all her documents like passport, pancard and bank accounts. Am I understanding correctly?

2) Should a marriage certficate consist only wife's maiden name? Is that the rule? I am asking this question because while googling on this matter across many websites I read some comments where it's said marriage registrer should always put maiden name of wife in the certifcate.

3) Can we revert wife's name from Amrita Suresh nee Ghosh to Amrita Ghosh (maiden name) in the marriage certificate ? If yes what's the procedure to do it?

Thanks again Sir.