generate steps with custom connector

Hi All, 

I'm creating a Custom Data-Connector to Connect to OPC (Oracle Primavera Cloud) which has a REST Data Service.
Although I can get the Connector to summon the data, I'm a bit wary of trying to implement query folding as I think it might be too complex and I'm trying to create a light alternative for myself and a couple of my colleagues.

 Basically the Proces currently works like this:

1) The user selects a Table in the NavigationTable

2) Based on the Column Information I generate a Json Body to request the Data from the Service

3) Using this Body a Table is fetched with ALL the columns and ALL the rows

I would like the users to be able to see and EDIT step 2 in the query. This way a more advanced user can opt to remove some elements from the JSON or add Filters and reduce the load size significantly. However currently in Power Query only step 1 and 3 are visible.

let
    Source = OPC_Connector.Contents(),
    Activity1 = Source{[displayTableName="Activity"]}[Data]
in
    Activity1

Is it possible to generate steps inbetween so the user can edit them later on?

Alternatively, is it possible to throw in a "column selection" / "Filter Selection" step in the GetData process?