Object Mapper is the declarative Salesforce Industries tool designed to map data between objects during key business processes. For this scenario, two mappings are required. The first maps the custom line item object 'A' to the custom asset object 'B' during assetization (when an order is fulfilled and an asset is created). The second, reverse mapping from 'B' to 'A' is crucial for MACD (Move, Add, Change, Disconnect) operations, where an existing asset is used to create a new modification order, ensuring custom data is carried back to the new quote.

A. Writing an APEX Hook is a custom code solution. The declarative Object Mapper should always be the starting point as it is the standard, upgrade-safe method provided by the platform.

B. This is incomplete. A one-way mapping from the line item to the asset only supports the initial assetization and will fail to bring the custom data back during MACD operations.

C. The correct tool is named "Object Mapper," not "Field Mapper." Field Mapper is a component within the Object Mapper configuration, but this option uses incorrect terminology for the primary tool.

1. Salesforce Help, Industries CPQ Developer Guide, "Object Mapper". The documentation details its function: "Object mappers map fields from a source sObject to a target sObject... For example, when you create an asset from a quote line item, fields are mapped from the quote line item to the asset."

2. Salesforce Help, Industries CPQ Developer Guide, "Asset-to-Order Field Mapping". This section explicitly discusses the need for mapping fields from an asset back to a quote line item for MACD scenarios, confirming the requirement for a bidirectional mapping configuration.