@Input() data: CivilLiabilityQuestionnaireModel;
public questions: CivilLiabilityQuestionnaireModel;

this.questions = { ...this.data };

const questionGroupIndex = 0;
const questionGroupItemIndex = 0;

this.questions
    .questionGroup[questionGroupIndex]
    .questionGroupItems[questionGroupItemIndex]
    .answers[0]
    .value = form[val];

// This works
this.questions.id = 'hotdog';

// This doesn't work
// ERROR TypeError: Cannot assign to read only property 'id' of object '[object Object]'
this.questions.questionGroup[questionGroupIndex].id = 'hamburger';

this.questions = {
  ...this.questions,
  questionGroup: {
    ...this.questions.questionGroup,
    [questionGroupIndex]: {
      ...this.questions.questionGroup[questionGroupIndex],
      questionGroupItems: {
        ...this.questions.questionGroup[questionGroupIndex].questionGroupItems,
        [questionGroupItemIndex]: {
          ...this.questions.questionGroup[questionGroupIndex].questionGroupItems[questionGroupItemIndex],
          answers: {
            ...this.questions.questionGroup[questionGroupIndex].questionGroupItems[questionGroupItemIndex].answers,
            [0]: {
              ...this.questions.questionGroup[questionGroupIndex].questionGroupItems[questionGroupItemIndex].answers[0],
              value: form[val]
            }
          }
        }
      }
    }
  }
};