Where is the customization and extendibility of zoho inventory?

Where is the customization and extendibility of zoho inventory?

After delving into zoho one subscription to test out systems we need for our business, I'm really disappointed after working in Zoho Inventory. Its features and customizability are extremely lacking compared to the other tools like CRM.

In our case we would be making use of zoho inventory and composite items as a workaround to have basic manufacturing assembly.

We manufacture drinks and edible products, in an bundle (assembly) we have an estimated output based on our composite item (recipe/ingredients). However we need to be able to modify the final output of the bundled quantity WITHOUT it altering the total cost of building that bundle. There are sometimes product loss or manufacturing issues that we can't account for until the production is finished.

So in our bundle we are planning to bundle lets say 100 units, but after the physical production finishes we may only get 92 units. Or we may get 104 units. 

A simple bandaid solution might have been to add a custom field to bundles "Actual quantity received"
Then when inventory levels get updated after you save your bundle it would use the value from your custom field. But there is no option for custom fields for bundles. 

How might one got about achieving something similar?

The customization seems to be quite lacking in the zoho inventory product. And even in the zoho inventory developer portal options are limited.