Before, the "file directory" setting of a file field in a bundle is set as "field/file". Now, I want that every user uploads his files into own directory, so I need to add a token in the "file directory" setting. But I'm afraid that the files uploaded in the old nodes can still show normally? If not, how to fix it?
Those files will still be shown normally unless you remove their directory manually, because the file path is stored in the database with each file information. So even when you change the folder for new files, the old ones will still know the path where they were uploaded.