If you have a D Endorsement that is about to expire:

You can do the Renewal Course as long as your D Endorsement is not over 1 year overdue by the date of training.

You will need to do the Beginners Course.

If you only carry a small amount of Dangerous Goods to do your work:

There is an exemption for dangerous goods transported for Use of Tools of Trade, Agricultural Use or a Commercial Purpose that is NOT for hire.  You can review it here under Schedule 1 and Schedule 2.

Having your D Endorsement gives you a valuable broad knowledge on regulations and requirements for transporting dangerous goods.  The D Endorsement can be used as proof you are trained and competent to transport these goods as per the Health and Safety at Work Act regulations.