[Vuejs]-How to modify deep vuex data with v-model

You won’t be able to use a computed property for this. Don’t use v-model, instead bind to :value and register your own event listener.

https://jsfiddle.net/jamesbrndwgn/L27pcksn/88/

You may also want to read about normalizing state shape. It will make working with Objects much simpler and avoid deep nesting.