Location Substitution in the Item 
Location substitution (plant substitution) in the item is a special variant of the rules-based ATP check (RBA) that you can use for standard items in the sales order. This function causes the following system behavior when there is a location substitution: If the rules-based ATP check for an item results in just one substitute location (the product remains the same), the system uses this substitute location for the item. The system does not create a subitem. If there are several location substitutions with different locations, one location substitution is selected either automatically or manually, and its location is used for the item.
This special RBA variant is also available for the subitems that are relevant for requirements in a sales bill of material in the sales order (item category group LUMF) and behaves similarly: If the RBA results in just one substitute location for a subitem of the sales BOM, this location is used for the subitem. (The location of the main item remains the same.)
Note
Note that the standard RBA (in which subitems are created for location substitutions and product substitutions) is not available for subitems of sales BOMs.
You activate the location substitution in the item in SAP ERP at item category level.
It is then available for the ATP check in the sales order and for batch backorder processing. However, it is not supported in interactive backorder processing.
Prerequisites
Required Product Versions
Location substitution in the item is available as of SAP ERP 6.0 and SAP SCM 7.0.
The following table lists the Notes (or the corresponding support packages) that are also required:
Settings in SAP ERP
To enable location substitution in the item, you must choose one of the following options in the RBA Control field:
Subitems Not Allowed, Plant Substitution in Item Allowed (D)
If you choose this option, the system is only allowed to substitute the location in the item. It is not allowed to create subitems.
Subitems and Plant Substitution in Item Allowed (E)
If you choose this option, the system decides whether to substitute the location or create subitems. It bases this decision on the check instructions, the rules it found, and the availability situation.
To make this setting, in SAP ERP Customizing choose 
Sales and Distribution 
Sales Sales Documents Sales Document Item Define Item Categories 
.
Settings in SAP APO
As of SAP SCM 7.0 with SAP Note 1832840 (or the corresponding support package), you can make a setting in SAP APO in the check instructions so that subitems are not allowed. By doing so, you cause the behavior of the RBA with option Subitems and Plant Substitution in Item Allowed (E) to be the same as with option D. You make this setting in the check instructions in the Create Subitems field by choosing Never Create Subitems (N).
Features
Handling Product Substitutions
During rules evaluation, the system can also find product substitutions. How the system handles these product substitutions depends on which option you have chosen for the item category in the RBA Control field:
Subitems Not Allowed, Plant Substitution in Item Allowed (D)
If you have chosen this option, the system filters out the product substitutions and only considers the location substitutions.
Subitems and Plant Substitution in Item Allowed (E)
If you have chosen this option, the system considers all substitutions. If there are product substitutions, the system does not execute the location substitution in the item, but creates subitems instead.
Determination of the Substitute Location
The standard RBA procedure is used to select the location substitution whose location the system is to use for the item. This selection is either done automatically by the system or manually by the user (manual selection is only possible in sales order processing in SAP ERP).
The procedure depends on the RBA scenario, as follows:
Multi-Item Single Delivery Location (MISL)
In a MISL scenario, the system tries to find a location that will enable all items of the same delivery group to be fully confirmed (see Multi-Item Single Delivery Location). If the system finds one, it copies this location to all items in the delivery group. If not, the settings in the MISL rule (Action After MISL field) define how the system is to proceed. For more information, see SAP Note 1854965.
Only One Substitution Allowed
In integrated rules maintenance (transaction /SAPAPO/RBA04), you can specify that only one substitution is allowed. If the system finds a substitution, it uses it, provided it is a location substitution that is at least partially confirmed.
Preselection of Suitable Substitutions
If you use the preselection of suitable substitutions, manually select the location substitution in Sales Order Processing on the Preselection of Suitable Substitutions (Simulation) screen or in the results overview. For more information, see Preselection of Suitable Substitutions.
In Batch Backorder Processing, you must use the Business Add-In (BAdI) Executes Preselection of Suitable Substitutions Automatically (/SAPAPO/ATP_PRESELECT). If location substitution in the item is active, the example implementation Example Implementation Substitution Preselection (/SAPAPO/CL_EXM_ATP_PRESELECT) returns exactly one location substitution (the first one it finds that is at least partially confirmed).
NoteIf location substitution in the item is active, the system automatically sets the number of substitutions to 1 in the import parameter IT_INTREQGRP of BAdI method SELECT_SUBSTITUTIONS.
End of the note.
RecommendationIf you have already implemented your own BAdI implementation and you want to use the location substitution in the item, check if this BAdI implementation meets your requirements.
End of the recommendation.
Default
If the system does not find a location substitution after executing the respective standard procedure, it uses the first location substitution with a partial confirmation.
Remaining Requirement
Since no subitems are created when the location is substituted in the item, the entire requirement is assigned to the item.
Requested Location
With location substitution in the item, the requested location for the item is not kept. Therefore, the system can no longer try to cover the requirement in the requested location during backorder processing.
Partial Delivery
There can be a partial delivery for a standard item in the sales order or for a subitem of a sales BOM in the sales order. In this case, the location of the standard item or subitem can no longer be changed. You can run a product availability check for the standard item/subitem, but you can no longer run a rules-based availability check.
Location Substitution in the Item of a Sales BOM
For sales BOMs, note the following:
Main Item of Sales BOM
The system does not adjust the location of the main item. The location in the main item can therefore differ from the substitute locations in the subitems.
Reexplosion of Sales BOM
The system does not trigger a reexplosion of the sales BOM based on the location.
Item Category Group ERLA
A rules-based availability check is not possible for sales BOM subitems with item category group ERLA.
Delivery Group Correlation
Delivery group correlation with one delivery date is possible. However, quantity correlation with correlated schedule lines is not supported.
NoteFor delivery group correlation with one delivery date, you must choose the value Form delivery group with one delivery date (X) in the Create Delivery Group field.
End of the note.
Delivery Split
The subitems can have various locations that differ from the location in the main item. The shipping points can therefore also vary. We therefore recommend that in the copy control for deliveries for a main item, you use a condition that does not include checking the shipping point. You make this setting in SAP ERP Customizing under
Logistics Execution Shipping Copying Control Specify Copy Control for Deliveries .
Storage Location
In SAP ERP, you can enter a storage location for a sales order item. The storage location is transferred with the sales order item to SAP APO. When the RBA substitutes the location in the item, the storage location is deleted from the item in SAP ERP.
Results List of Batch Backorder Processing
You can use the results list filter, which is available in the BOP results list (transaction /SAPAPO/BOP_RESULT) and in the BOP monitor (transaction /SAPAPO/BOP_MONITOR), to define which items you want the results list to display. You have the following options:
Items for which the location has been substituted at item level
All items except those for which the location has been substituted at item level
All items
You make these settings on the filter tab page Location Substitution in Item.
In the Results List, you can add the columns for the old location (location of the item before substitution) and the location type of the old location to the layout.
More Information
SAP Note 1854965