Terrestrial radio uses frequency division AND geographic separation in order to provide communications ability to the users on this planet. To tinker with the ionosphere would increase propagation even for those signals for which propagation beyond line of sight was not a significant concern. Not every user needs over-the-horizon signaling. To a very large degree, we use the horizon effect for useful things- for one, it allows us to have multiple 100KW television transmitters all using the same channel all on the same continent. Ionospheric changes will have negligible effect on the power needed to adequately cover a metropolitan area with signal, and may actually INCREASE the power needed to swamp a distant signal that's intruding spatially into another market.