That's right. BMW, for example, you need software tool like the dealer has or similar. With it connected to the vehicle, it has a bleed function for the ABS, where it activates it while you do the bleeding. It gets air that otherwise would be trapped in the ABS unit out. If there is air in there, it's impossible to get it out without the tool. On the other hand, air only gets in there if you let the reservoir go empty or open lines at the ABS unit, etc. So if you make sure the reservoir is full, can switch a caliper quickly, you would be OK with just normal bleed procedure.