Hi,
I'm not sure I understand your question correctly. Contingency reserves are already included in the cost baseline, therefore the cost baseline will not be affected/updated.
In fact, when a risk occurs and calls for the use of a contingency reserve, the estimates will be updated, and the overall contingency reserve will decrease. The baseline, however, will not change.
An exception I can think of is if the contingency reserve allocated to that risk is not sufficient to implement the planned risk response, so management reserves may be needed. This will indeed require a change request; but - as you recognise - this is needed because management reserves come into play.
Gabriella