If a product is imported as well as exported, it has to be classified under both the customs tariff of the importing country and the nomenclature used in export declarations. Even if the same nomenclature and, therefore, the same type of numbering scheme are used for both imports and exports, traded commodities have to be classified twice.
In the EU, the customs tariff number is always an extension of the CN. The Member States may use the TARIC as it is or add digits in a national customs tariff. It might therefore make sense to let SAP GTS derive the CN code from the TARIC code at the time of classification. Business users classifying a product select the appropriate TARIC code, and the system proposes the additional classification with the CN code contained in this TARIC code.

To enable the derivation of CN codes from TARIC codes, you have to assign the numbering scheme representing the TARIC to the numbering scheme representing the CN in the Reference Scheme field (SAP Global Trade Services, edition for SAP HANA → General Settings → Numbering Schemes → Commodity Codes → Define Numbering Scheme for Commodity Codes).
Caution
The derivation of a commodity code from a customs tariff number is not possible in reclassification.