Can we set hideNavbar property after form has been created?

Doesn't look like it from the help pages, but I would try something like

Form.hideNavBar = true

No, didn't work

Not sure why you would need to set that later

It depends on when the form will be load

Can you determine that logic before creating the form ?

No

Why not, what type of logic would you need after the form is created to determine if you want to hide the navBar or not

Well you are right, we can do that.