It depends on the goal of the exercise... you are right that sissification is strictly defined as 'humiliation' and therefore looking and acting female is not the aim but humiliation is. However, I have heard the terms used more or less interchangeably - sissification referring to a process where the sub looks and acts female all the time at the end of it and those undergo this process referring to themselves as 'sissy subs'.

In some cases it may start out as humiliation play - lets put the large, clompy man in a dress and lingerie and have him serve drinks at dinner - but progresses into a more full time, serious situation where the 'large clompy man' learns how to dress and do make up properly and even undergoes body modification (which can be as basic as a weight loss programme to lose the beer gut) to look even more female.