On Music Crator 6, let us say I record my drum track, then I want to set the velocity of the snare at 60 throughout the song. I go to Piano Roll view and click the piano key that corresponds to snare. All the snare notes are now selected. How do I set a velocity for the whole group?

Not sure about PRV since I don't use it..... but in staff mode.... right click a note and the drop down offers that option.  I think you can also do that with a group of motes by highlighting the group.
 
It's been a very long time since I worked with midi at the basic level. I used to do it alot in my early days but now tend to work with audio tracks mostly.

Is this what you're asking about?
 
http://www.cakewalk.com/Documentation?product=Music%20Creator%206%20Touch&language=3&help=DrumEditor.13.html