Risks: You facilitate the creation of yet more inefficient work practices which ultimately necessitate more overtime payments. Ding, ding, ding. The overtime payments are the problem people.
You pander to aging PS/CS emplyees, giving them extra time off (unpaid) without affecting their pension entitlements. Ding, ding, ding. The pension entitlements are the problem people.
These 2 groupings appear to me to be the most intransigent with regards to change. This solution, and the threat to extend these arrangements indefinately, are no threat atall. This could potentially be just another bag of carrots with any savings being born by the consumer through withdrawal of, deemed, less essential services with ultimately no real reforms taking place.