Change the value of a field using Logic?

Hello to All,

I'm creating an access request form where the requester has to enter the needed role. He also have to answer a question by yes or no. If the requester selects Yes, he has extra information to enter.

The yes/no field has a default value set to No, as this is the most common answer.

The thing is that if a specific role is selected, the answer to the question is always Yes. So I would like the field displaying Yes and being locked. I found the way to lock the field using the Logic, but it does not seem possible to change the field value.

Does anyone know if this is possible ?

Thanks a lot,

Fabrice