if you have more than one SIP installed it is possibel to change the default SIP by modifiy the Registry. SipShowIM() shows/hides always the default SIP.
The installed SIPs are listed here: HKCU\ControlPanel\SIP\installed\ (refer the CLSID under HKCR\CLSID for details).
The default SIP is set here: HKCU\ControlPanel\SIP\DefaultIM=<CLSID_of_desired_SIP>.
Also you can use the OS function: BOOL SipSetCurrentIM(CLSID* pClsid).