I have not tested this with the TCP protocol.
But in general I can think of 2 different ways to respond with a second message.
1) Customise a normal VSM (eg. created from RRPair) that responds with 1 single message.
Then in the VSM add an additional step that responds with a second message.
2) In the VSI it is possible to configure 2 responses. The VSI shows on the right hand side:
Transaction Basics
Request Data
Match Script
Response 1 of 1
For this last tab (Response 1 of 1) click the + sign and add a second response.