All faders on the Spitfire GUI can be assigned to a CC value of your choice. If you have a MIDI Controller you can customise these parameters to your own preference.
1) With a library interface open, find the fader you would like to re-assign. In this example, we will reassign Vibrato from CC#21 to CC#71.
2) Right click the fader on the interface.
3) You'll see that by default Vibrato is assigned to CC#21. First choose Remove MIDI Automation to unassign CC#21.
Following this, you can reassign the fader by selecting Learn MIDI CC# Automation.
4) It may seem as though the nothing is happening, however if you move the controller that you want to use you'll find that the fader will automatically reassign to that value.