Input tag's disabled attribute is one of the rare 'valueless' attributes...It means that it's value is irrelevant, as long as the attribute presented it will render the input tag disabled...
All these have the same effect:
<input type="text" name="name" disabled />
<input type="text" name="name" disabled="true" />
<input type="text" name="name" disabled="disabled" />
You may introduce an if statement around your textbox and render once with disabled and once without...