Ok, this request has been added to the tracker:
https://winscp.net/tracker/1051

Hello,

I second this request.
Imagine the following use case:
You know a file is binary and want to open it in a hexadecimal editor. Naturally, you right-click the file, but find no Edit (alternative) entry in the context menu.
Well, unless you know the feature is in the File menu, you're wasting time opening the preferences editor to swap editor order.

Well, noone asked for this before. Will consider it now you ask :)

I wonder why this is not implemented.
We can do this from File > Edit (alternative) but It would be more quicker to have it on right click context menu.