See ==>>
Calibre: Mac keyboard shortcut to move file to end of list
I've only wanted to reorder the text files in an EPUB on rare occasions. When I have it's taken me several attempt's to get what I want using drag-n-drop in Sigil (didn't use calibre to do this because it will offer to merge files if you drop one file onto another)
Until today, I didn't know I could do it with some fixed shortcuts in calibre… see post #5 in above link. But it has limitation on Mac due to lack of an End Key.
You'll see I suggested a Move flyout menu, I suggest the same could be provided in Sigil.
Suggest rename the existing
Move... to
Move to..., and label the suggested flyout menu to
Move within -> Up/Down/First (or Top)/Last (or Bottom) - whether they should have shortcuts I'll leave to you, but if they're provided I suggest they be configurable and default to None.
BR