I successfully added a new column "Category" to the Quotations Tree and the Create\Edit pages using the instructions on
https://doc.odoo.com/book/2/3_CRM_Contacts/contacts/#customizing-partner-fields
I was also able to edit Quotations of Customers and fill values for the new field. But, when I launched the ERP portal after 2 days the columns no longer are visible also the developer mode was not active.
Do we have to perform some specific action to make the changes permanent.
Please ignore the URL pasted in the query above. The documentation link is as below:
https://doc.odoo.com/book/2/3_CRM_Contacts/contacts/#customizing-partner-fields