They must have continual radar guidance to impact their target. Therefore, simply turning off the guidance radar is enough to prevent the missile from guiding to any target. I think your "very basic understanding" is a little out of date.
http://www.fas.org/man/dod-101/sys/missile/sm-2.htm
Link
Block IIIB is the next step in the continuing evolution of the Standard Missile family, incorporating an infrared (IR) guidance mode capability developed in Missile Homing Improvement Program (MHIP) with the radio frequency (RF) semi-active guidance system of the proven SM-2 Block IIIA. The MHIP dual-mode RF/IR guidance capability is being incorporated to counter a specific fielded and proliferating electronic warfare systems in existing aircraft and ASCM threats. OPEVAL of SM-2 Block IIIB was conducted during April 1996, with missile firings by an Aegis cruiser that was completing workup training for deployment. Based on OPEVAL results, SM-2 Block IIIB is operationally effective and suitable.
Um hmmm. And if your understanding were anything more than basic, you would realize my statements in post 46 are both current, and correct. The MHIP for the Standard missile uses a side mounted IR seeker to aid in terminal guidance for the RF guided Standard missile. It is used to increase missile accuracy at the endgame against targets using certain jamming techniques. It is not used to acquire and guide Standard missiles to their target.
The reason IR guidance can't be used in long or medium range missiles is because there are limits to what an IR missile seeker can "see" at long range. Even the newest IR missiles have a relatively short range and are mostly within visual range weapons.