It would be unfair to forbid that as people with more than one KS accounts could buy multiple pledges. We decided that you can buy multiple pledges but either:
1)You will be charged shipping for every pledge and receive all freebies that comes with them
2)You will be charged only for shipping of your highest pledge and you receive freebies only from the highest pledge.
Example: You want to take a bundle reward (160$) and a lv3 reward (250$). You should pick lv3 reward as your choice and pledge 410$. In pledge manager you will be able to use extra dollars to choose an additional bundle pledge. After that you will be able to choose if you want to pay both shippings and receive 4 freebies or pay shipping only for lv3 pledge and receive 3 freebies