What brand of clay is that? And how durable would you say it is?

I'd suggest making it two parts united by tiny magnets, it's not gonna work if it's just one part unless you make it a hat that goes above the widest part of the head (even then, it could fall off if it's off-centered). For that kind of hat, I wouldn't do it in just one piece, it wouldn't work if it has a narrow point as well

You’re gonna have to carefully and strategically cut around that to make it two parts or something

You trapped yourself good there.