How to query only specific id's in a custom source plugin
This was quite easy by adding a $query-&gt;condition() to public function query() using IN and NOT IN in dynamic queries
This worked to exclude certain id's:
$products = [1, 2, 3,];
$query-&gt;condition('product_id', $products, 'NOT IN');

This worked to include only certain id's:
$products = [1, 2, 3,];
$query-&gt;condition('product_id', $products, 'IN');

I was then able to clean up the yamls, and only query the stuff I wanted.