Is there a way of not overwriting a track?

If I want to re-record say a specific section of a track - either MIDI of Audio in GB, but I don't want the new recording to overwrite my previous audio material (either audio file or MIDI notes), what setting do I use to turn overwriting off so that as i'm recording it doesn't clear everything away? So I mean, whatever i record will just be added to what's already there.Thanks