Additional expanders for account aggregation

Why is there not an easy way to add additional expanders to the API call? We have a use case where we use another employee attribute, can that be easily added to the OOTB or would we have to use a custom connector?

For reference: Aggregation Settings

We ran into this a little while ago also with the Dayforce connector and couldn’t find a solution. We ended up switching to a custom WS Dayforce connector

Have you guys run into a problem with any rate limiting when trying to aggregate accounts?