A lot of engineers use circuit breakers like switches. Using them to reset systems all the time. Eg I brought an A320 in with a popped fuel pump breaker. These are a no no reset until the circuit has been checked. Engineer came up whilst I was writing it up pushed the breaker back in switched on the pump for about 10 sec & then asked for the log to sign it off.
Carrying engineers for observation is great but do not let them touch anything. Air & ground are not the same in terms of consequences.