I don't think changing feather for different conditions makes sense. Flat water paddling is where the stroke is the same each time, and repetition is how technique is ingrained. Over time the brain learns very specific patterns in which to fire the many muscles involved in the paddle stroke. It is very hard to change these patterns, as anyone who has struggled to unlearn bad technique can attest. When things get intense in rough water the body (which actually means the brain) is likely to revert to whatever it has been trained to do. If that is a high feather flatwater stroke and the feather has been lowered significantly, things might not go well. I recall that when Oscar went from a normal feather to zero feather he made increments 5 degrees at a time and it took something like a couple years to make the transition.
On the subject of zero feather paddling, I have only played around with it a little. But my understanding from what I have read is that it really requires abandoning single hand dominance. With each stroke each hand switches roles from being the control hand to being the loose hand. So it is not just a matter of twisting less as would be the case going from 60 to 45 degrees; it is an entirely different way to paddle.
Current Skis: Nelo Vanquish AIR, Epic V10g4, NK 670 double, Epic v8 double g2, Think ion g3, NK exrcize, Carbonology Feather, Think Jet, Knysna Sonic X
Former Skis: Epic v10g3, Kai Waa Vega, Epic V12 g2, Epic V12 g1, Epic v10 double, Nelo 550 g2, Fenn Elite S, Custom Kayaks Synergy