is it safe?

Nice "marathon man" reference .  I am a newbie so I have no experience in this area yet, but I've been doing a lot of reading and I seem to remember folks saying that indeed it can be done but often the pastels disappear after the application.  I would think that a nice, gentle airbrushing would work just fine. 

It is quite safe...and the pastels don't "dissapear". Pastels have a very very "flat" effect when they are freshly applied. This effect is what makes pastels look really good. But, if you put a coat of flat clear over the pastels, you will lose the original flat effect, but not the color of the pastel.