Reloading directories with a lot of files

When reloading the directory is it possible to only reload the files that have been added? I.e If I have a folder of 1000 items and I add 1 song, I don't need to reload all 1000 files again.

You could drag&drop that 1 file into MP3tag (and press the Ctrl key while you do so) while the other 1000 are still loaded
Otherwise MP3tag would have to look at all the files again as it is possible that other applications have modified the data.
In general loading of already known files speeds up if you use the library function, see File>Options>Library.