I want to keep my usual schedule, and I'll tell my boss I plan to quit if they change it.
Is that really okay? It's usually quite normal to obey the boss's orders.
I really just want a high paying job.
It's very reasonable to want to have a predictable work schedule. You should be able to set boundaries like this in the workplace.
I'm quite stubborn and won't change my mind about this. I really don't think I'm being unreasonable.
These days, finding a high paying job can be quite difficult and I know you are really into your comfort zone. But a job's a job and at the end of the day we all have to listen to our superiors. Being stubborn about it may cause a lot of problems and potentially jeopardize your position.