For example when querying a screen in an app, can I only return the text of an object and the center_y coordinate?
So far I've gotten just the text by using the query :
query("CalendarCellView", :text)
but can I get just the text and center_y fields returned in the results hash (without editing the hash myself)?
It isn't. There isn't support for multiple selectors at the moment, which would be necessary to select multiple parts of the output. There aren't even selectors for some elements at all - see the answer in this post Calabash iOS: how to get value using query command. I don't think there is a selector for center_y.
This leaves you with a map or select as the only option.