First of all, my son did fine with a transfer & major change that did require taking some summer courses to fill the gap for some general ed requirements – he was able to find online community college courses that qualified, and cost was very low. (He paid, not me – and this was in California which does have pretty clear guidelines about transferable units — but the point is that it is doable).
But my main point is to agree with @momofsenior1 – a parent is under no obligation to finance all of that. The main thing is to make that part very clear. My son’s actually had a 3 year gap between the first 2 years and final 2 years of his college at the school where he transferred, and that meant that he had run out the clock on parental financing. (I basically had set an expiration date on parental-college support.). He did fine and actually graduated debt-free.
I also had a sibling who had an erratic educational course – so that is one reason I placed clear limits on my son. It is much better if your son graduates with a major that fits his goals, whenever he graduates — but it doesn’t mean that you have to bear the financial brunt of all his mistaken choices along the way.