After cutting and hinging the mask blank, I put it on a sculpting armature and decided that I wanted a slightly longer muzzle. I ran masking tape around it to make sure I was cutting straight and then cut it off with a Dremel. I added a few strips of Wonderflex to the inside and, once it was shaped properly, hot glued the end of the muzzle in place and checked the closure on the jaw. After a few small adjustments, I mixed up a tiny amount of Smooth Cast 300 and drizzled it into the gap over the Wonderflex. Once it set, I used the Dremel to sand it down smooth. The change was minor, only 3/4" but it looks better in profile now for the character I'm working on.