Acrylic paint is water based and does not adhere well to oil based undercoats. You could try a bit to see and wait a day to see how durable the bond seems to be, but I amm pretty certain that you will find that it just lifts away from the pastel surface. . If you want to produce a permanent / long lasting finish you should use a proper acrylic primer.
Best wishes - Majikthise. .
My guess is that over time the acrylic will crack and flake off.
thanks !! :)