Enhance Moodle Question Bank Import/Export Functionality

I need the following modification does to moodle question bank import/export feature: 1. Add a new varchar field named externalqid in question table. This field must be visible in Question entry screen as well along with name field. 2. Modify the Moodle XML version of the export functionality such that in the export file, externalqid is be emitted for each question. i.e. a new child of question named value should be present. 3. In the import functionality, the externalqid (if available in the import file) should be first used to check if a question with same externalqid already exists in the database. If not, proceed with the import normally i.e. create a new question in the DB. If it does exist, then update it with the new data in the file i.e. do not create a new question. For example, if the existing question has four options and the question in the file has 5 options, update the original 4 options in the same order and add a new option. This must be done in Moodle version 2.4+. You can build and test it your own moodle installation and give me back the new/updated files. thank you!