Agree with all the other PP - you know what you need to do, even if you are knackered.
If it’s of use, a phrase I’ve found really helpful is ‘you need to be able to trust what I say’. Sometimes my four-year-old understands that, and sometimes he doesn’t, but it always helps me to say it.
It reminds me that my job is not to make him happy, it’s to provide a safe and secure place for him to test boundaries, learn and grow, and that the one thing he needs from me is sincerity, to know that I’m telling the truth and not misleading him. So in our house, we say yes a lot if we can, give choices to help frame decisions and then when we say no, we mean no.
And if that sounds a bit worthy and Pollyanna, I’ll be honest and say that sometimes I just yell ENOUGH and go to a different room to calm down.
They adapt really quickly to it, I don’t think this will be as tough as it might appear. I reckon you’ve got a week of hard work, then it’ll be done.