@KrisK, I think this is the wrong road to go down at the present time. The entire concept of inventory kits is that all items are stocked as completed items. They are only sold together for convenience. (Radio controlled car + 2 AA batteries = Car Kit. The car does not include the batteries because they could expire before the car is sold.) While it possible to use inventory kits in other ways, such a kit that sells 1/12 of a case of wine instead of having a separate inventory item for individual bottles, what you are talking about is more complex.
Future evolution of inventory kits may not take place with your use case in mind. So you might find your entire workflow broken. It seems easier given the current state of the program to use the clone feature on production orders, which are meant for the purpose you describe. When a change occurs, edit the most recent production order as you clone it, giving it a new finished item. You should be creating new inventory items when there is a part change anyway for good configuration control. Of course, it is easier if you clone a production order that already is set up for the right quantity. (Standardizing production lot size could help there.)
I deeply sympathize with your frustration over the lack of a bill of materials that can be called up and multiplied by the number of finished items desired. But that is already in the ideas category: Production Orders - Enhancements. Unfortunately, it was the very first idea placed into the category when the ideas tag was introduced in 2017. It languishes there still.
There is also another suggestion already in ideas: Suggestion: Allow use of Inventory Kits with Production Orders. Further comments belong in that topic, so I am closing this one.