On macOS, one can set the "Open With ..." application in the information panel of a file without changing the default for this file type. However, doing this for a number of files is very tedious. A simple case is to change all .txt files in a directory to a special editor, but leave the system wide default (usually TextEdit). I have tried AppleScript, command line tools as well as a minimal GUI app (using LSSetItemAttribute), but all fail because of a lack of permission. Is there any way to achieve this?