How to handle multiple action mappings?

[hshackle]

This may be a very simple question, as I'm new to MIDI controllers and still trying to understand the "philosophy" behind them and how they should be used. I have an Akai MPK49, with various faders and knobs. I would like to map these faders/knobs to actions in Reaper, but I would like to change between different mappings depending on what I'm doing - i.e., a knob might be assigned to modify a VST setting if I'm working in a VST, or assigned to some other setting if I'm editing a track. What is the proper way to accomplish this in Reaper? I've noticed that each knob/fader has 16 different channels - does that mean I should have 16 different "sets" of mappings? Or is there something else I should be doing?