The purpose of the Maple Syrup is to give the faster some calories to burn and a bit of nutrition and minerals. The fast is already extremely limiting your caloric intake and you don't want to lessen that or you will be setting yourself up for a fall. Your metabolism will go into starvation mode.
The book on The Master Cleanse says your intake should be 6 to 12 10oz glasses of the lemonade mixture per day. In each of those glasses is recommended 2 tablespoons of Maple syrup which is about 105 calories. The books says you can lessen that if you want to lose weight or take more to gain. I have been following the instructions precisely and have lost 20 lbs in 17 days.
If you are interested in The Master Cleanse and want the best results you should stick to the program as written or at least very close. That said, if you want to change it that is your choice. But if you chose to change the ingredients or anything else about The Master Cleanse please let people know that you are following your own modified version of the fast, so that folks don't get the wrong impression.