It is possible to hide either entire class systems or individual classes and/or characteristics via the Extras > Edit class system window.... [Alter class system...] These can still be displayed in the part information of a component if required, but are otherwise not selectable or are not specified.

You can find information on the setting under Section 5.12.12, “Create or edit your own class system ” in eCATALOG 3Dfindit