You can certainly use fresh herbs in your Cajun seasoning instead of dried ones. However, fresh herbs have a higher water content, which can affect the texture and shelf life of the seasoning. You will need to use more fresh herbs compared to dried herbs. A good rule of thumb is to use three times the amount of fresh herbs to achieve a similar flavor profile. If using fresh herbs, keep in mind that the moisture reduces the shelf life of the seasoning. Store the Cajun seasoning in an airtight container in the fridge to help preserve its freshness.