Wizard schools that can bypass legendary resistance?

[Aquillion]

Except no illusion can do anything like that.

Well, Phantasmal Force could, but it requires a save, which defeats the purpose of using it to answer this question. Also perhaps Mental Prison.

Also, I think you could do it with Seeming, if you counted the shackles as clothing or equipment.

I think you could probably try using other illusions that way? Nothing strictly forbids it. "An illusion of shackles binding that guy" seems like a valid use of Silent Image, provided the shackles could fit within Silent Image's area limits. The real question is...

That assumes the enemy is kind enough to stand perfectly still between the casting and the Malleable Illusion. In combat, that's about never.

Malleable Illusion is a Bonus action. So the question is whether your victim can move enough between your action and bonus action to get out of the shackles. That's really a DM call.