Programmabile MIDI drum pads

One feature which I've tried to look for and have not found (so I am assuming it isn't already a feature) is the ability to program the drum pads on my MIDI keyboard to perform whichever drum function I want as the pre-set doesn't include some of the parts of the kit that I frequently use. If this feature was implemented, I feel it would be of great benifit to all who use the drum kit while composing. I haven't tried to see if this was a function since before the drum line update, so I apologise if I haven't realised that it is already a feature.