Part of what the OCPD listing does is confirm a specific Time vs Current performance. OCPDs are tested at various current levels to insure they will "trip" in the correct time frame, based on a specific ambient temperature.
You may load a breaker to any amperage level you want (as long as it is below the breaker AIR level) for a time period which will not cause it to trip, and in my opinion it is not a violation. In fact there is nothing that says you cannot trip a breaker. But, if the breaker is tripped regularly you will have to also consider it's mechanical and electrical life.
However, you may not overload the wiring.
Basically, the NEC says: size the load; then pick the wiring; then pick an OCPD which is not larger than the wiring.
