oh wow nice trick, I just tried to look up some exmaple on ffxiah, but I just found that people call cheat cure set to be items with -hp ? haha the other way around?
I believe you can do it that way as well, you can remove HP by lowering your max HP with gear that has -hp stat and then swap back to your other gear which will raise your max HP again and you can cure to bring yourself back up. Might be a little riskier to drop your HP rather than raise your max HP. I'm not sure how many -hp gear options there are for PLD, seems easier to find +hp gear.
Than again, my PLD is lvl 20 so I will happily admit my ignorance and let someone else answer properly if I'm misinformed.