Would you do a change request if specific risk didn't occur and therefore, you didn't need the related contingency reserve?

It depends on how the financial contingencies are calculated and funded.

If for example, contingencies are calculated as EMV (impact*probability), the assumption is that all risk contingencies together are statistically sufficient to cover all the risks considered. No single risk event could be covered by its own contingency alone. So, even if a risk event is not longer possible, removing its EMV from the budget is not supported by the underlying statistics.

Sometimes, funding for contingencies is outside the project budget, then indeed, the contingency commitment would be relieved (but the budget or project baseline does not change, except maybe the risk level).

Soha,

I agree that decision makers generally don't like to deal with small project deviations. In the scenario you described I would create a table showing the risks that didn’t occur and the contingency funds I could return to the funding center. I’d then post the table somewhere and inform the decision makers about it, explaining that I’ll keep the funds within my project to cover unknown unknowns unless they request them back, and that I would update the table throughout the project. This gives the decision makers the option to reabsorb the funds at any time while avoiding the hassle of processing many change requests. In my experience most decision makers have no problem leaving the unused contingency funds attached to the project until its conclusion.