Is collaring a circuit breaker considered deactivation by the FAA? Let's say you discover that your landing light is inoperable during the preflight. Your aircraft doesn't have a MEL, so you follow 14 CFR §91.213(d). Assuming you do everything else required (placard, etc.), would placing a collar around a circuit breaker be considered deactivation? 

If not, is there anything that a private pilot can do that would be considered deactivation?
Based on this Advisory Circular, the answer is yes.


  g. Deactivation means to make a piece of equipment or an instrument unusable to the pilot/crew by preventing its operation


Collaring the circuit breaker prevents it from being pushed in, and therefore prevents its operation.