AS far as i know, my province sent my employer an email, mentioning that my employer need to notify the province if there is change to my job. But if the employer does not notify the provincial immigration, they will never know. So you should not be worry. Also, if you are switching the same NOC job, even if they know, provincial immigration will still support your nomination. If you almost reached the final stage of your PR, you should not to notify these changes, as it may causes huge delay to your application