You use 4into1 splitters upstream of the FTS.
Full details of the FTS:
I don’t understand that. What is a realistic sequence of printing that would get them swapped over in a meaningful manner in the middle of a print?
@Eponymous
Two objects printed using opposite filament combination e.g. PLA+PETG supports and PETG+PLA supports in per-object sequence?
Is this a meaningful effect? Without the FTS it would still print in the same time with the same filament use.
For example, bottom half of part is green with red accents, and top half is red with green accent. You use left nozzle for main color and right for accents, that will improve printing time
I give up. No-one even understands the question, let alone the filament track switch. 