Hi Deep,
Firstly, to activate inspection material - batch combination, you can do the same from material master QM view. In the 04 inspection type, you can choose / configure the desired inspection controls, like below:
You have mentioned several other cases above.
If you use co-product, your yield (quantity) on the major material will be lesser, but the complete cost will not be incurred on the same. The order settlement will happen to both the materials. Just create a co-product scenario, create and order and go to Header->settlement rule. You can see both co-product items in the list. you can set 70% cost to one and 30% to another.
If the physical production (at the end) is 70%, then ideally you should follow the same process. There's no point in producing to 100% and then converting 30% from it.
Other option you have asked for is to create new orders after the actual GR. You can either do that, or create a trigger point on confirmation so that the new order is auto created upon confirmation.
If you want to continue with your current option, then just need to change the QM settings to create the inspection lots.
Thanks
Prem