Make custom fields in Quoted Line Items readonly

Dear all,

I'd like to know if it is possible to make some custom fields readonly in a quoted line item ?:

For example the Product Category field.

I added in the field custom\modules\Products\clients\base\views\quote-data-group-list\quote-data-group-list.php the following code : 

by setting readonly property to true, but it doesn't work. I did another trick while changing the field product catalog, but it does not fit to my needs.

Is there something I'm missing ?

To be more precise, I'm on a Sugar ENT

Thanks in advance for all your answers.

Best regards,