We have some background processing on form and in the result, some of the form fields can become null. So how should information message about this action look like? The best option we have "The value of X was set to blank".
If I am understanding your question, there are some fields on your form that when information is entered, override some other fields that are no longer needed (for example, use saved phone number vs. enter a new one)
Second if the user has already entered input, you probably do not want to clear the value from the disabled field and instead just ignore that field when submitting. That way if the user were to change their mind, they could go back and continue editing the field without having to type everything all over again.