In LoadComplete, you can replace parameters in Rich Internet Application requests with variables that contain data extracted from preceding responses or data LoadComplete generates or gets from external files:
Find the POST request, whose parameter value you want to replace with a variable.
Switch to the Request page and go to the Request Body tab at the bottom of the page. You will see a tree-like structure of request parameters:
Find the needed parameter.
In the Variable column, click and select the needed variable in the resulting dialog or enter the variable name manually in the
Select File > Save from the LoadComplete menu to save the changes you have made.