A power utility will not reduce the power it delivers by changing frequency. This explains what you can get away with using the decades-old technology the power grid is made of - i.e. not very much:

http://www.edn.com/design/components-and-packaging/4369085/Using-a-power-transformer-at-a-frequency-it-wasn-t-designed-for

(executive summary: any significant change and BANG!)

But reducing voltage is effective, safe, feasible and often done.