How to unload single filament

Hello,

as there must be both heatbreaks loaded with filament (to avoid backflow of filament into a empty heatbreak), i am curios how to unload/change a filament role?

I guess i have to heat up the hotend for that, but when i then pull out one filamemnt, is then the other filament not backflowing in to the now empty heatbreak?

The wiki/documentation only states something about “cold” loading filament before heating-up the hotend the first time, but there is no advice regarding filament unloading.