Midi plug-in ( to only play a random % of the beats in a loop)

I guess you do this in CAL.
 
Copy/paste the code below into notepad, and save it as RANDDEL.CAL, select your track, use Process->Run CAL and navigate to the file you've saved.
 
Note this will delete random notes, so make a copy of your original track before running it.
 

;
;Delete random notes
;The higher the strength, the more notes are deleted
;
(do
 (int iStrength 1)
 (getInt iStrength "Strength 0 - 10 :" 0 10)
 
 (forEachEvent
 (if (== Event.Kind NOTE)
 (do
 (if (<= (random iStrength 100) (* iStrength 10))
 (do
 (delete)
 )
 )
 )
 )
 )
)

 
I guess, you could change the (delete) to change velocity instead, or even change the first if statement to narrow the selection down to certain notes (e.g. hi-hat).
 
Here's a good guide on CAL:
http://members.ziggo.nl/t.valkenburgh/Cakewalk%20Application%20Language%20Programming%20Guide.pdf
 
Mark.