Lize, why do you say it will reject me? I am simply putting my intention in a legal format? Shouldn't that actually strengthen my application?
you have to provide EVIDENCE that you will return to your home country, Not a paper signed by you saying that you will not do it. There's no misconduct by doing this , but it looks extremely phony to add such paper in your application.
It's better to show ties with official documentation.( bank statements, property documents , real stuff , not something you write in 5 minutes).
If somehow that can strengthen your application , everyone would be doing it.