I don’t know how you are sending the data but it seems to me if you have control of it why not simply build a VRL record with the headers and output it first?
I don’t know if this is what you were thinking but you were right I just did a =column name and mapped it to a new vrl file but then I realized it would duplicate that every time a new value was sent over. I would just need that header value one time not every message.