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It should be as long as iOS 6 is still being signed.
Just put your iPhone into DFU mode.
Then restore and option/control click restore then click on the latest iOS 6 IPSW
 
Apple is still signing SHSH for 6.1.3/4 so you may restore back before the 18th which is most likely when they will close the window. For safe measures restore before the 17th in case you might not have time before then and get stuck on a iOS you don't want.
 
I've noticed that the modem firmware of the iPhone 5 on iOS 7 GM changes from "3.04.25(iOS 6.1.4's modem firmware" to "5.00.01". will this affect anything when the jailbreak for iOS 6.1.4 comes out?

From previous experiences i've had with downgrading your firmware. I've notice that the current firmware's modem firmware remains at the latest version and not revert back to an older one.
 
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