modify existing attributes in file of records in OIC

Content

We are reading a response from a Webservice call  which returns array of json element structures and writing into a file in OIC as new record.

How ever some attributes in each record are null and need to populate them by calling a webservice .

How to address this sceneario ? If we use write file again with append option it will only append from the end of file but not modify the existing records / attributes..

Or Can we access 2 collections / arrays in a single for each when writing a new file.