To load a custom file with enzymes click the Enzymes file button and browse for the file. The file must be of the Bairoch format.
For details about the format refer http://rebase.neb.com/rebase/rebase.f19.html.
To export enzymes use the Export enzymes button. You can also save the currently selected enzymes to a file and load saved selection. Click the Save selection and Load selection buttons correspondingly to do it.