Hi @imageekgirl,
In addition to what @vdespa noted, you can create a json string, store thats string as an environment variable, and when you need to use that json string to modify it, you can parse that JSON in your test pre-request script using JSON.parse(pm.environment.get("jsonString"))
, to which it should act like native JSON, where you can add, remove, or modify JSON attributes and values, and then save it back to your postman variable like so: pm.environment.set("jsonString", JSON.stringify(yourJSONvariable))
which should persist it for the next request.
Then repeat this process for any future requests that need this JSON.
Best,
Orest