Overview
Custom Ontology is a module that allows you to add custom vocabularies when standard ontologies such as LOV, schema.org, and W3C are not available.
For basic usage of this module, please refer to the following.
https://nakamura196.hatenablog.com/entry/2021/07/24/235050
For how to update vocabularies that have already been created using this module, please refer to the following.
This article explains how to add classes and properties to an already created vocabulary.
Method
We assume that a custom vocabulary called “myprefix” has already been created as shown below.

myprefix
When adding new classes and other elements to this vocabulary, leave the “Create a specific ontology” form empty.

As a result, you can add elements as shown below.

References
Please note that if a vocabulary has already been created, filling in the “Create a specific ontology” form will cause an error as shown below.

Summary
I hope this is helpful when using Custom Ontology.