Can you change the tempo of MIDI?
Changing the tempo will affect the midi, its playback speed the least. You should be able to just change the tempo in the DAW and that should do it.
Can you fade MIDI in Ableton?
You can create fades on an audio file or automate the volume of the instrument rack or effect rack. You can even fade the master track in or out using a Utility plugin. The same applies if you want to fade in a drum rack etc.