We are going to be getting a soap API call from our SAP instance when an event is triggered. They are able to send us model number, but nothing else. The image urls and product names are stored in a table in our AC Classic marketing instance.
Is there a way to enrich any of the data coming in through a soap call if they cannot pass everything that is needed in the transactional email template?
Assuming your message center execution instance is not the same as your marketing instance (I've seen this too many times), use your marketing instance as a reverse proxy to the message center instance. I.e.:
SAP calls custom soap interface on marketing instance with model number
Marketing instance js looks up the number and makes a call to message center exec with the data it collects
Message center sends message
Step 2 should have user-facing configuration and read the nms:extAccount table for info about exec instances- avoid hardcoding things in general.