@jlastofka
This is pretty much how I used to do it and to some extent still doing, havent heard the name ’witness’ though I thought more of it as a sacrificial piece.
If you can program the printer to stop at a desired height you dont have the need to watch the printer, dont have to be nervous about missing it and usually I can start the print looking quite good if I may say so myself.
But, this thread is not about how to change the filament mid print per se, it’s about a programmed stop at a certain height.