It's not necessary to convert your CASA or CAANZ licence to a DGCA one.
If you get a job in India the company employing you will put you through the FATA (Foreign Aircrew Temporary Approval) process, this generally involves:
- Ground school for the company
- DGCA medical
- DGCA FATA exam (fun times)
- DGCA interview (which is actually 10-15 minutes of verbal testing on your aircraft an Indian Law etc)
Once issued the FATA it is bound to the licence of origin you applied with (CASA/CAANZ) and you will be required to keep that licence current. If you are operating as a line captain then it's just your licence and IR, TRI/TRE you will also need to keep those current as well (very hard to do with CAANZ).
In my time there I looked at getting the full DGCA ATPL but realised on many levels it was not worth the pain, hassle and time. In fact you'd be better off doing an FAA or EASA licence instead.
Hope it helps.