I'm a developer and not too familiar with GATP process.
In our retail project we have BOMs for drinks with deposit bottles. Now we have to handle the product and/or location substitution in GATP.
Consultants told me that the deposit bottles are not marked as ATP-relevant because they come with the drink anyway. In SAP standard a substitution will create a new sub-item and change the item type of the original header item as not relevant for anything (pricing etc.).
As mentioned in SAP notes, the required BOM explosion is not done, consultant say this would lead to a 3-level hierarchy (original item, substitution item as sub-item, new deposit bottle as sub-item of sub-item). 3-level hierarchy could not be handled.
Also, we are asked by the customer to overwrite the original item with the (rule-based) substituted item putting original material/amount/location into item Z-fields.
I don't know exactly what kind of modification and user exit handling will be required to make the whole process work correct.
We are working on a sandbox release with GATP done in SCM system.
I'd be happy to gain some insight or just to hear about experiences with such (standard) situations.