Updating a CoreData entity of an existing iPhone app

I'm working on updating a fully functioning iPhone app (written in obj-c) that is already available on the App Store. It's a navigation-like app with a map and "points of interest" that the user can add to a list (much like favorites). All POI data are received by the app through a web service and divided between different core data entries. I want to extend one of these existing entities and give the user the ability to update/delete/save new attributes in it. The attributes will be user-owned an don't need to be put back on the server: they have to be stored locally on the device. I'll be providing the interfaces layout in Xcode storyboard together with the project, so there's only need of coding in obj-c and hook the interface. The project uses pods, so the candidate has to be familiar with cocoapods; sources will be made available through BitBucket. I'm quite familiar with obj-c myself as I developed most of the app, but due to lack of time an knowledge in CoreData, I need help to implement this new part of the project. I will follow and support the developer during development through Skype and email. Attached is a PDF with schematics about the current scenario and what I'm looking for. Thank you.