Can PBF4 send different MIDI message for the fader while one of the buttons are held down?

Have you seen Kristóf's video where he shows how to do something very similar? You should be able to apply the same approach to the faders.

If you only want it to happen while held down, keep the button mode set to momentary (which is the default) and then use a Press/Release block to change the MIDI message value you want on the relevant fader element. You would change it to the new value on Press and back to the original value on Release.