Would anybody happen to know if I can cancel my remaining G.I. Bill payments and use the remaining 30 later on in my career?

Ask the VA in an e-mail and phone call so you have hard proof. Things are changing too much to simply rely on RP for this.

In order to use your GI Bill benifits you must submit your registered classes each semester to a VA representative at your school so that they can submit it for approval and processing. If this is not done you will not receive payment and do not use your GI Bill. It should be as simple as not reporting your classes to the VA. Because they damn sure don't give you money unless you jump through all their hoops.