Thank you all for your valuable comments.
Initially, I thought this was more of a process question and so could be solved out-of-the box without having to go into configuration and create new condition type like what Srinu has suggested (thank you nevertheless).
The goods will definitely be returned so returns goods receipt will be done. My proposal is similar to what Jelena has suggested; to create 2 separate credit memos.
(1) Create a returns order in VA01 for the original invoice which will then allow user to do returns GR when the goods get ships back. Then create credit memo for this returns invoice which will be same amount as what we originally billed customer.
(2) Because the credit for returns in (1) pulls data from the original invoice and does not allow me to edit the items (correct me if I am wrong), hence the amount; have to create another credit memo in FB75 just for the additional charges (not only freight but also other miscellaneous charges like handling costs, etc.).
Would this be a viable solution?
I am more concern about the effects in Finance as I am not familiar in that area.
