Is it possible to introduce new dimension columns while data ingestion in druid

Hi -

Is it possible to introduce new fields as part of dimensions while ingesting data in druid. Currently I have a Avro file that I ingest using flattenSpec but I also want to add 4 new fields with some hardcoded values. I want to add metric columns based on these new columns.

The reason I am doing this is - I have 3 different files that I intend to load in a same datasource in druid and since there is no other column in these files that I can aggregate on I need a way to differentiate and aggregate the data in druid once all the three files are ingested. So my plan is to have 3 ingestion configs with 4 additional columns in each that get set differently for different file and then add metric columns based on these dimensions that I will introduce.

Is this possible to do and if so how?

Thanks