I don't like to pop into discussions when I don't have much to contribute, but I'm not really sure how this would fix Malamar's Swagger problem. From my perspective, all that it accomplishes is "allowing" Malamar to waste an action to fix a situation that the item's coding could have prevented from being an issue, while simultaneously turning any other stat boosts into liabilities. Furthermore, this means that, during this free action for the opponent, another Swagger can be applied, bringing Malamar back to square one, so to say, or Malamar can be pressured by any particularly strong attack, which forces it to sacrifice any prayer it had of keeping the damage race competitive.Another suggestion I made earlier in discord would be allowing Malamar to target itself with Topsy-Turvy.
In other words, the drawbacks of this effect seem to heavily outweigh the reward of using Topsy-Turvy in the first place, without even mentioning all of the problems Malamar could run into with Taunt, Encore, and other disruption tactics.