Akhil,
Also you might consider the Eventing Service it can be very performant to do bulk transformations. For example: N1QL CBQ Update million records is not working - #5 by jon.strabala
Note although Eventing does not use a sub-document API it still might be the right solution.
Essentially get a copy of the entire document super fast via DCP and are free to use JavaScript to manipulate it as much as you want in a fast v8 lambda and then you write the entire document back when done.
Best
Jon Strabala
Principal Product Manager - Server‌