The brief answer to the question is, yes you can most certainly determine which mapping service to invoke without using TN.
The longer answer is yes but why avoid using TN for this task? One of the primary tasks of TN is to determine the desired action based on a document type, document contents, sender, & receiver or some combination. The scenario you describe is precisely what TN is designed for.
You need to decide which sort of maintenance tasks you want to live with. Undoubtedly the number of partners and document types will grow over time. When you add new partners and/or document types, do you want to edit and deploy a service or do you want to edit profiles and rules? The answer to this question may be derived in part from the underlying motivation of your post–what do you hope to gain from “avoid(ing) the first submission to TN?”
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