Code:
        for as in self.ANIMATIONSEQUENCES:
            if as[1].find(":") != -1:
                start, end, step = as[1].split(":")
                frames = range(int(start), int(end)+1, int(step))
            else:
                frames = as[1].split()
            i = 0
            for f in frames:
                self.framelist.append([as[0] + str(i), int(f), as[2]]) # name, number, type
                i += 1
find this part of the script by looking for the first line. make the following changes then you will be able to enter a range like 1:100:2. the last number is the step size.