Yes, you can change it definitely. All that matters is that you were employed at the time of submitting the application. Here's the official requirement:
Be employed in Canada with a valid permit or authorization to work pursuant to the Act and Regulations at the time the application for permanent residence is received and must not be self-employed, unless working as a medical doctor in a fee-for-service arrangement with a health authority. The employment must meet the definition of work under subsection 73(2) of the Regulations;