BPMN21 — Extend BPMN with a element that subclasses an existing BPMN element

'Section 8.2.3 Extensibility' on page 57 of the BPMN 2.0 specification states:

"The BPMN metamodel is aimed to be extensible. This allows BPMN adopters to extend the specified metamodel in a way that allows them to be still BPMN-compliant."

On page 58 it is stated that:

"Every BPMN element which subclasses the BPMN BaseElement can be extended by additional attributes. This works by associating a BPMN element with an ExtensionDefinition, which was defined at the BPMN model definitions level (element Definitions)."

Question:
Is it possible to extend BPMN with an element that subclasses an existing BPMN element?

For example, is it possible to extend BPMN with a new task element that subclasses the BPMN Task, similar to how e.g. a ManualTask or UserTask subclasses the BPMN Task? If this is possible, could you provide an example?