If you hold an Indian DGCA CPL then you will need to write the Specific exam
Only if you are converting your foreign license you dont need to write the Specific exam ( as of today but this rule can change in the near future )
You only need a ground class certificate if A/C you want to endorse has an all up weight of more than 5700 KG
Refer CAR , Section 7 , Series B Part 1 , ISSUE II 12th November 2010
7.6 Extension in the Category of a Pilot’s License
The applicant should have:
(a) Current license in the relevant categtory
(b) The aeroplane having all up weight more than 5,700 kgs or twin engine
helicopter are required to undergo Ground Training Classes on
Technical/Performance on the aircraft from DGCA approved Training
Institute.