As one of the resident Habsburgophiles, I will be the first to say that obviously this is totally and utter impossible.
But in all seriousness, a war between the Austrian and Spanish branches of the family is going to be incredibly hard to create. A war between the two branches would more or less destroy several hundred years worth of carefully crafted Habsburg tradition and myth, something that is likely neither side would have wanted. Plus it's just not practical, who the frick are the Spaniards gonna marry if they don't have female Austrian cousins?