Not sure if it’s useful but here’s a script similar to File > Import > References from Bookends. Contrary to the internal command the script imports only the selection and adds also custom metadata. And as it’s a script it can be customized of course.
-- Import selected Bookends references as rich text including tags & custom metadata
tell application "Bookends"
tell front library window
set theRefs to selected publication items
repeat with theRef in theRefs
set theID to id of theRef
set theDOI to doi of theRef
set thePMID to pmid of theRef
set theISBN to isbn of theRef
set theURL to url of theRef
set theLanguage to language of theRef
set theDate to publication date string of theRef
set theCreationDate to date added of theRef
set theModificationDate to date modified of theRef
-- set theType to type of theRef
set theTitle to title of theRef
set theNotes to notes of theRef
set theKeywords to keywords of theRef
set {od, AppleScript's text item delimiters} to {AppleScript's text item delimiters, ASCII character 10}
set theTags to text items of theKeywords
set AppleScript's text item delimiters to od
set theAuthors to authors of theRef
set theEditors to editors of theRef
set thePublisher to publisher of theRef
set theJournal to journal of theRef
set theVolume to volume of theRef
set thePages to pages of theRef
set theRating to rating of theRef
set theCitation to user1 of theRef -- user1 is the Bookends field where BibTex citation is stored
set theAbstract to abstract of theRef
set theContent to format theRef using "Summary.fmt" as RTF
set theFormattedReference to format theRef using "APA 6th Edition Markdown.fmt"
(* repeat with theAttachment in attachments of theRef
set theFile to the first attachment item of theRef
set thePath to the path of theFile
if thePath is not "" then
end if
end repeat *)
tell application id "DNtp"
set theRecord to create record with {name:theTitle, type:rtf, content:theContent, rating:theRating, comment:theNotes, tags:theTags, creation date:theCreationDate, modification date:theModificationDate} in current group
set URL of theRecord to ("bookends://sonnysoftware.com/" & theID) as text
add custom meta data theDOI for "doi" to theRecord
add custom meta data thePMID for "pmid" to theRecord
add custom meta data theISBN for "is?n" to theRecord
add custom meta data theURL for "link" to theRecord
add custom meta data theLanguage for "language" to theRecord
add custom meta data theDate for "date" to theRecord
-- add custom meta data theType for "type" to theRecord
add custom meta data theAuthors for "authors" to theRecord
add custom meta data theEditors for "editors" to theRecord
add custom meta data thePublisher for "publisher" to theRecord
add custom meta data theVolume for "volume" to theRecord
add custom meta data theJournal for "journal" to theRecord
add custom meta data thePages for "page" to theRecord
add custom meta data theAbstract for "abstract" to theRecord
add custom meta data theCitation for "citation" to theRecord
add custom meta data theFormattedReference for "reference" to theRecord
end tell
end repeat
end tell
end tell