Pass values to the Request body which is incremented

Hi,
I have to pass one of the property value into JSON file which increments for every request I have to trigger. For this I have written a Keyword which will read the Request body but the thing is I cannot make a parameterized Request Body. Pleaase advise.

String body = ’ { " header" { “menu” : “Item”, “goods”: " 2001" } } ’
From the above Json file, I have to change the value from 2001 to 2001. How can I do that ?