Is it possible to add to a JSON by typing it in the URL?

I am sure my question my might make much sense right away. But I short I am making in Ethereum smart contract, and for reasons too long to explain, I need to be able to make a get call to a URL and append my own data to the JSON file that will load from that URL.

This is probably not possible, but in the case that it is please let me know how to do it.

To give a concrete example, say I make a get call to "http://ift.tt/2eHi3Kg" this returns something like this:

{
  USD: 10.32
}

Can I add something to the URL so that when it loads I get:

{
  USD: 10.32,
  userId: 53
 }