Maplestory "High Five" Private Showcase

All this means is that you won't be able to roll % damage potentials on armor in the future. Changes like this aren't usually applied retroactively (for example, when they added a level req to boss damage potentials, those 30% boss Purple Surfboards didn't revert to 20% boss ones). If you have armor with % avoid beforehand, it'll become % damage unless they somehow force a reroll of just that line.

Judging from KMST patch notes, equipment's avoid related potential is removed or changed to other stats.
So don't count on it being changed to damage%.