The REST Connector supports the WITH CONNECTION keyword, which can be used to override URLs, query parameters and query headers in a connection. The POST body can also be overridden when the POST method has been selected for the connection. WITH CONNECTIONallows you to alter some parts of a connection rather than create a separate connection.
I've had to fight through this over the last week... our URL required 2 query parameters, both "start_date" and "end_date". In order to get that to work successfully, I had to set values in the initial REST connection setup, allow it to verify, and save the connection. Then in code, I had to do the following:
FROM CSV (header off, delimiter "|", quote """") "CSV_source"
WITH CONNECTION (
QUERY "start_date" "$(vCurrentStartDate)",
QUERY "end_date" "$(vCurrentEndDate)"
I'm sure there's someone out there that could use this with their connections. Good luck!