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.