I have a form made in InfoPath to create material requests at my office. One of these fields is a Choice Type with two options: Department and Project, this Choice Type is required. There is also a second Choice Type that becomes required if the previous one is Project. I have implemented this behaviour using an InfoPath rule.
Once an item is created I can edit it by a very similar form, which has the same fields of the creation form as well as some extra fields generated authomatically. (which I did not implement).
The problem is that on this form I can't change the first field from Department to Project or viceversa because there is no other option and I can't turn it back to blank because it has to be a required field.