I have created an instr. track with my addictive drums. Each time I grab a file in add. drums and will use it, Cubase aut. create a new instrument track under the existing track. How can I stop this?
So, you are wanting to drag the clip to the existing Instrument track?
Go to Preferences>MIDI>MIDI File>Import Options> and set Destination to “MIDI Tracks” rather than “Instrument Tracks” (even though that might seem illogical 
), and make sure that “Auto Dissolve Format 0” is not activated.
Super - thank you 
It works to an extent. It still renames the track every time you add your next midi piece.
If I name the track Drums, the next midi bit I drag and drop changes the name to what ever you dropped
for example 6-8 swing-beat 009. Not a show stopper but annoying none the less.