I just wanted to have one process for two tasks. They are same, but in one of them I have a checkbox "Add user" and in the other one I wanted to have the same checkbox (to save the whole logic of the process) but with the name "Delete user".
Thats why I was looking for a workaround and for finding a way to change the display name dynamically.
As a workaround I am using now two fields, one checkbox with no display name and one string, which value I am using to show as a display name and which I can change dynamically.
Anyway, I dont really need this as a feature.