[C#]
// This example shows how to change the class extension of an extension object or feature class.
// The extensionName parameter is used to set the Value property of a UID object; the string can
// be in ProgID format ("MyProject.ClassExtension") or GUID format ("{484F435C-9A08-11D3-815A-0080C78E8371}").
// The extProperties parameter should contain the extension properties (in many cases, there are no
// properties, and this can be passed a null value).
public void ChangeClassExtension(IObjectClass objectClass, String extensionName, IPropertySet extProperties)
{
  // Attempt to acquire an exclusive schema lock for the object class.
  ISchemaLock schemaLock = (ISchemaLock)objectClass;
  try
  {
    schemaLock.ChangeSchemaLock(esriSchemaLock.esriExclusiveSchemaLock);
 
    // If this point is reached, the exclusive lock was acquired. We can cast the object
    // class to IClassSchemaEdit.
    IClassSchemaEdit classSchemaEdit = (IClassSchemaEdit)objectClass;
 
    // Create a UID object for the class extension.
    UID uid = new UIDClass();
    uid.Value = extensionName;
 
    // Call AlterClassExtensionCLSID to change the extension CLSID. To leave the class without
    // an extension, both of the parameters should be given null values.
    classSchemaEdit.AlterClassExtensionCLSID(uid, extProperties);
  }
  catch (COMException comExc)
  {
    // Re-throw the exception.
    throw comExc;
  }
  finally
  {
    // Reset the lock on the object class to a shared lock.
    schemaLock.ChangeSchemaLock(esriSchemaLock.esriSharedSchemaLock);
  }
}

[Visual Basic 6.0, Visual Basic .NET, C++]
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