The SWIFT MX / ISO 20022 standards are based on XML. Therefore, you can add such components to the mapping in the same way as any other XML schema. There are no other special requirements to map such data.
The standard SWIFT MX schemas can be downloaded at https://www2.swift.com/knowledgecentre/products/Standards%20MX.
The standard ISO 20022 schemas can be downloaded at https://www.iso20022.org/iso-20022-message-definitions.
There are many non-standard schema variations of the ones mentioned above, such as country-specific variants. You can use any XML schema as mapping component in MapForce as long as it is a valid XML schema.
For a mapping example, see Example: Convert SWIFT MT to SWIFT MX.