| Argument | Type | Description |
| clsidOld | REFCID | The class to be emulated. |
| clsidNew | REFCID | The class which should emulate clsidOld. This replaces any existing emulation for clsidOld. May be CLSID_NULL, in which case any existing emulation for clsidOld is removed. |
| Return Value | Meaning |
| S_OK | Success. |
| CO_E_CLASSNOTREG | to be described. |
| CO_E_READREGDB | to be described. |
| CO_E_WRITEREGDB | to be described. |
| E_UNEXPECTED | An unspecified error occurred. |