is it possible to set default value for DE for tracker program?
Yes you can do it with Program Rule (with Assign value action)
@didate is correct. And remember that the program rule could evaluate always to true by using an expression such as that “true”
Umm I don’t know, But the solution I see is to use a second data element (Yes Only) which will make the first one editable when you check it.
The rule will be : assign a value as long as the checked data element is not checked