extend an Ontology

When extending an existing ontology…is it possible to override some of its
properties?
e.g.
   The following statement is found in an existing ontology

 <daml:ObjectProperty rdf:ID="hasInstructor">
  <rdfs:domain rdf:resource="#Course" />
  <rdfs:range
rdf:resource="http://www.daml.ri.cmu.edu/ont/homework/cmu-ri-people-ont#Memb
er" />
  </rdf:ObjectProperty>

and I need to override this property by using this statement

  <daml:ObjectProperty rdf:ID="hasInstructor">
  <rdfs:domain rdf:resource="#Course" />
  <rdfs:range rdf:resource="#Lecturing-Staff" />
  </daml:ObjectProperty>

where Lecturing –Staff represents a different description than ….#Member.

Thanks
Charlie