Вы можете взять записи и обновить свойство или посетить вложенные свойства.
const
update = (target, source) => Object.entries(source).forEach(([k, v]) => {
if (v && typeof v === 'object') update(target[k] = target[k] || {}, v);
else target[k] = v;
}),
injectionObject = { pages: { about: { title: 'Changed About Page' } } },
currentObject = { pages: { home: { title: 'Home Page', description: 'This is the home page' }, about: { title: 'About Page', description: 'This is the about page' } } };
update(currentObject, injectionObject);
console.log(currentObject);
.as-console-wrapper { max-height: 100% !important; top: 0; }