There are two general functionalities that let you do this in MDP2, Channel Changers and Pedal Boards. You can google both of those (include “midi designer” in your search terms) and also check the manual at midiDesigner.com/manual. The first thing you should try to achieve is a channel changer knob that controls which channel your buttons are on. Then you can add buttons to move that knob around, probably with another knob as a supercontrol to turn those channel (function, in your case) changing buttons into a button group.
This stuff is pretty interesting to get your head around and see if it even applies to your case. How I work, and recommend you work, is to set up some sloppy buttons (just one or two channels) and get the concepts working. Then you can build from there to your final goal (8 buttons, several functions, stuff looking nice, well-labeled, etc.). I don’t recommend getting everything looking nice and then trying to get the “engineering” to work. There’s also a chance that I’ve misunderstood the question, or that your MIDI target (Ableton? Logic?) doesn’t respond as you expect. So... experiment a bunch before building anything serious.