omit() will remove any fields specified from the message and then send down the pipeline. It currently only works for top level fields (i.e. address.street would not work).
omit({"fields": ["name"]})message in
{
"_id": 0,
"name": "transporter",
"type": "function"
}config
omit({"fields":["type"]})message out
{
"_id": 0,
"name": "transporter"
}