>>35518905I was worried about this too, so I experimented with Zygarde a bit to see what I could dig up. Turns out that in SM and USUM, there's an option to fuse Zygarde with Cells instead of breaking it down. This means you can preserve the nature, ball, ribbons, moves, and shiny status while switching from Aura Break to Power Construct.
However, to do this, you're going to need 50 Cells on standby, so if you've already assembled Zygarde with all of its Cells, you're fucked. Of course, this is assuming the distributed Zygarde won't come with Power Construct anyway.
Consequently, this also means that a 10% Zygarde with Aura Break in any ball other than the standard Poke Ball can't exist.