Can I change an object's category once created?

Once an object's category is determined it can not be changed to a category outside of it's classification. This is because an object's classification determines the fields available to an object.

For example, an object classified as "Transportation" is going to have different fields compared to one classified as " Paintings, Drawings, & Prints".

To see all the categories and classifications you can view them in your account settings>configurable fields.