It would be hard to imagine where even an executive order directly from the president will stop something as prominent as gun violence. The key thing to remember is that the criminal element will not respond to such an order. What difference will this make to someone who wishes to rob your home at gunpoint? It just means that they may have to alter the process in which HOW the rob you.
The real effect of president Obama's orders will only be determined long term in scale of money: How does this order affect gun sales? Will a larger black market open for criminals? Will this discision lead to an increase of violent crimes that do not use firearms?
Only time will tell, but the definitive answer is this: crimes will not cease, or even slow down, just because gun "control" is reorganized. Crime will continue to be rampant, it just may use another means.