Customize the output of the Drupal 8 Aggregator module I am using the Core Aggregator module to aggregate content from RSS feeds, and then using a View to output the content.

The Aggregator module has two view modes, default and summary. The view modes themselves are editable, but the feed items themselves are grouped into the "items" field, that has no options.

In default mode, the title, blog, description etc. for each item are rendered, but in summary mode only the title and blog name are rendered.

How can I influence the fields that are rendered in summary view mode?
I believe what you are looking for is the 'Manage Display Option" viewable from 

admin/config/services/aggregator/display

In other words from the aggregator admin ui.

Not sure how much control this gives you in reality. Also I am having issues with Aggregator appearing to strip out image tags from my feeds for some reason, so I am also considering using the feeds module instead that seems to have better support than the core module.

UPDATE 

Ended up using the migrate module which enables custom mapping of fields from a field to a content type of your choosing with custom fields etc.