That is my thought too. As much as I don't want to break things, I'd rather not do it during a panic situation. I also wonder if one just does this from the start, once a year so, if that ridge just won't get created in the first place. Change the fluid, a little at a time but often.
Not sure how much fluid is held inside the ABS unit? It's a long ways away from anything that would let in moisture, and from heat. I'm not sure how important it is to really change it--now if air gets in there, that's different. But I just change in the m/c and then pull some from each wheel.
I like the vacuum pump method, easy, although I had better results the first couple of times, lately it just pulls a lot of air around the bleeder for some reason.