If you need to use your vehicle for a commercial reason one time, or a few odd times here and there, it's not necessary to worry about vehicle rating. One-off situations are acceptable and don't require commercial vehicle insurance for proper coverage.
For example, suppose you drive your car to your retail job each day and typically never use it for commercial reasons, but your boss is running behind one day and asks you to drive a few boxes of product over to another store location just this one time. In that case, there's no reason to be concerned about insurance coverage. Even if you did happen to get into an accident while driving those boxes over, your insurance company would not penalize you for a one-off situation, and you would still be able to access the insurance compensation you would generally expect from your personal car insurance.
While a one-time use may not be an issue, every insurance company is different, so make sure to speak with your Morison Insurance broker and let them know if a one-time commercial use could be an issue.