Need an EL expression to make a filed read only for change assignment transaction.

Summary:

Content (required): We need an EL expression for the person type to be read only field (defaulted to Employee), While performing the change assignment transaction for an employee. When the transaction is performed for a non employee we don't have any restrictions.

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):