Installing the 14T will only require you to pull the wheel axle 1/2" back in the dropout, which should not be a problem unless you are already within 1/2" of the end of the dropout with your 16T. However, my question to you is why you would want to use a 14T FG cog, which is huuuuuge. What is your front chainring, anyway?

Yes, flip/flop is the way to go for a combo SS/FG.