Tax calculation: Fields in TTE

Hi all, I have a nice one here.

Backgound:

We are implementing a CRM 5.0 Stand alone order-entry with Middleware connection to SAP FI. TTE is working well, we find all the taxes we need, as long the TTE looks at attributes in the masterdata (Products, Business Partner).

Problem:

Now the customer wants to overrule some tax findings in the case of an order cancellation (we talk about an airline here ;).

In our prozess analysis we defined new transactiontype (cancellation order), which is a follow-up document of a standard order. Now, this means that all masterdata remain the same and the TTE calculates the same parameters (Tax rates, Tax IDs, etc.).

Since we dont want to double our products, we need a controlling attribute in the order document to tell the TTE that something has changed (e.g. an tax event).

For us the TTE seems to have a very limited context, but maybe we have overseen some feature, since it is relatively new to us.

All help is appreciated and Thanks in advance.

Guido