Electrode Potential Half Reactions Does flipping a reaction as written change the sign of the value of E or is it a completely different value? 

For example if I have the value for the half reaction $\ce{Cl2 + 2e- -&gt; 2Cl-}$ but need the value for the opposite reaction ($\ce{2Cl- -&gt; Cl2 + 2e-}$), do I just put a negative sign and treat it like $\Delta H$ values?
Yes, you are correct - just flip the sign. As quoted from the venerable UC Davis ChemWiki:


  To determine oxidation electrodes, the reduction equation can simply be flipped and its potential changed from positive to negative (and vice versa).


They give the value for your (forward) reaction as +1.358 V, so for the reaction in question, you'll use -1.358 V.