Hey,
your assumption is correct! You have to define the property “hst:componentclassname” with the full name of your custom class (eg. org.example.CustomComponent) for the component node under the hst:catalog in the hst configuration of your project.
If you are replacing the class for an existing component you would have to update the property also for any instances of that component under the hst:workspace and within the available containers.
Kind regards,
Lef