CUSTOM TYPES A custom type identifies the data format and meaning of a value that is not represented by a friendly type name ...

CUSTOM TYPES
A custom type identifies the data format and meaning of a value that is not
represented by a friendly type name built in to BCDedit. Custom types are
typically used to extend the functionality of BCD.
A custom type has the following format:
     custom:OxXXXXXXXX   The literal string "custom:" followed by an 8-digit
     hexadecimal number that encodes the format and meaning of the type.

A custom type appears in the same parameter position as a friendly type name in
a /set or /deletevalue command. For example:
     bcdedit /set {} custom: 0xXXXXXXXX 
For information about custom types that can be used with this version of
BCDedit, search the Microsoft Knowledge Base for these keywords: BCD, BCDedit,
custom types