Identifier is always renamed to an attribute name e.g.
attribute name: My Attribute
attribute identifier: first_attribute
becomes:
attribute name: My Attribute
attribute identifier: my_attribute

Steps to reproduce

Steps to reproduce:
1. in a clean eZ Publish installation create a custom class with attribute name "My Attribute" with identifier "first_attribute"
2. Save the class
3. Apply patch for #19024
4. Edit the class and click "Apply" button
5. Note that "first_attribute" identifier got renamed to "my_attribute"