How to make a conditionally editable READONLY textbox?

In my form, there is a textbox named 'slug' which generating slug depending on 'headline' field (I used jQuery to display auto-generated 'slug'). Now, I will display the slug text field as readonly but if any user want to edit 'slug' if needed then he/she will able to edit it before submit. How is this possible?

I am using Bootstrap for form design and I am using Laravel framework to code.

via Chebli Mohamed