How to duplicate a display (which is not the master) as a different display type?
Drupal 7 solution
There is no out-of-the-Views-box solution for this in Drupal 7 ... Except if you get really creative (or via &quot;ugly ways&quot; as @MPD wrote in a comment below the question) with exporting / editing / reimporting such view. But that's not out-of-the-Views-box of course, and  to my knowledge not included somewhere within the Views UI. Comment #1 in the issue about &quot;Clone a Page view into a block view&quot; seems to confirm this.
Drupal 8 solution
In Drupal 8, for an existing display of a view, assuming it's a page display, you can say &quot;duplicate this display as another display type&quot;. This will copy all of that view definition to the new display.
As an example, in a standard (core only) Drupal 8 site,  you can now duplicate a page display as:

another page.
a block.
an attachment.
an embed (1).
an entity reference (2).
a feed.

This appears to be one of the most exciting new features of Views in Drupal 8 ... Apart from Views in Drupal Core (= VDC) ... of course.
Notes:

(1): In the Views settings, if you select “Allow embedded displays”, then they can be used in code via views_embed_view().
(2): In the Entity Reference field settings, select “Filter by an entity reference view” and use a view with this display type to define what can be referenced.



Credits: &quot;Babou&quot;, who made me discover it while listening to &quot;Talking Drupal (episode 111)&quot;.