With a few minor safeguards, yes!

"Okay, but I do have some conditions to it," Natsu finally agreed. Erza quirked an eyebrow.

"Oh? Okay then, lay them on me," Erza nodded, crossing her arms.

"Well, first of all, no ordering me to hand Lucy over to you... At least not permanently," Natsu noted, and Erza pouted.

"You say that as if I would do that, though at least you're covering a base there," she conceded.

"Okay, good. Also, no gagging me to prevent me from saying the safe word, or at least accept frantic muffled versions of said safe word as me saying it," Natsu added. She nodded, finding that reasonable.

"Fair enough," she replied. "What else?"

He considered for a moment, and finally asserted, "And no making me order Lisanna or anyone else I potentially have in the harem to do anything they wouldn't want to do."

"Ah, good catch, Natsu, though I think the safe word would cover that part," Lisanna noted.

"Don't want to assume anything," he replied, rubbing the back of his head.

Erza nodded in agreement. Natsu was smart to implement some safeguards... and her mischievous side was actively thinking of ways to test how far she could push Natsu around them.

Once they hashed all that out, Natsu made the wish. The key word to trigger Natsu's implanted submissive side would be "My pinkette bitch." Natsu had protested a bit when Erza picked it, but ultimately decided to allow it, albeit with some grumbles.

As for the safe word, that was simply, "Dragon's pride." Once Natsu had made the wish, Erza turned to him, and grinned. "So, shall we get started, my pinkette bitch?" she asked him, making him moan as she triggered his new submissive side.