Hi GTS Gurus,
As per my experience in my previous project we use to re-transfer the Commodity Codes to ECC system from GTS (8digit Codes) as suggested by Dave.
in GTS Cockpit, while classifying the products(T-code:/SAPSLL/PR_CLWB_CUS) we use to select the Option 'Adopt Derived Numbers', which used to derive the Commodity Code Numbers from the Tariff Code and it will be transferred to ECC using re-transfer program. if you want to transfer the 8 digits of the code from the 11 digits of Tariff Code, you can try this option exist in the above mentioned transaction.
hope this might be helpful , correct me if i am wrong.
Thanks,
Srinivas Yellampalli