So back in high school when I built my first Fett suit, I bought a set of vacuuformed armor. I think it was sentra? Anyways, the armor was all smooth and had no preformed dents. So I found a neat way to make dents and make them look blaster burned. Sorry I dont have any pics, but I will explain as clearly as I can.
Before painting, I held a lighter under the backside of the armor where I wanted the dent. I held it just a little ways form the actual armor until the area underneath turned black and the plastic became pliable. I then gently pushed from the top of the armor until the dent was the depth and size that I wanted. I then let it cool off and it hardened up again. Then, after making all the dents I wanted, and after painting, I used my finger to smear some of the soot form the underside of the armor where I had held the lighter and rubbed it around the area on the front of the armor. It came out looking like realistic blaster burns. I dont believe you could use this techniques with anything but sentra armor though. But I liked they way it turned out. Hopes this helps!