It was always allowed.
If you have models with strategically placed colours, say “there’s no color1 above 130th layer” you switch color1 to color5 that starts at layer 520… basically whenever’s there’s actually no more than 4 colours per layer you can switch colours around. However the slicer will only see 4 colours when slicing. And if there’s rapid change you shouuld add pause between layers to give yourself some time to actually switch the filaments.