You can directly change the SubUser Id in the API request, there is no restriction of changing it from our side. You can manipulate it as per your requirement.
Also, you can change the SubUser Id directly in your MyAccount.
1) Go to Integration( Demo)
2) Go to Show Advance Inputs.
3) Edit the SubUser Id to specifically identify the parsing.
If you have any questions, you can always contact RChilli support at email@example.com.