peter Generally you can not import a song that already exists. The song name is not derived from the filename so you don't need to rename the file but you need to delete the song first before importing it again. The reason for this is that when you get a bunch of songs in one file from a band mate for example you definitely don't want your own songs with the same name overwritten.
Generally you get a prompt if you want to overwrite the song or all songs or do you want to add them in which case the software automatically creates the same name but adds either a number at the end to indicate version or it places a copy1, copy2, love me tender1, love me tender2 at the end , this gives the user choices that make importing very quick and easy.
If there isn't a clash with same name files it just does the transfer, thats how it should be to make things move quicker.