Yes, Definitely heat it. It'll break if you try to cold bend it.
I should mention, make sure you have the right nipple for that gun before you make any changes, I believe the Cherokee/Seneca use a different nipple than the standard TC 1/4x28,, and because of that folks end up putting revolver nipples on them because they are more commonly available.
Here it is, a 12x28 stock number PTC-S
http://www.trackofthewolf.com/List/Item.aspx/159/2/PTC-S If you do bend it;
A bit beyond dull red, not as hot as cherry red will do, the metal will let you know.
Remove it from the lock of course, then I usually clamp it in a vice as a heat sink and heat just the curved neck,, bend just a tiny bit at a time and repeat as needed.
I've never had the need to re-temper an adjusted hammer, or quench it, I let it cool a few minutes then run under water so I can handle it an that's it. The S curve and geometry of the hammer keeps it strong enough, any case hardening is just for looks.
When it's fully on the nipple,, it's preferable to have the hammer face strike the nipple with full on diameter. Use a marking compound (inlet black/lipstick) on the nipple then lower the hammer to contact,, lift the hammer and look inside the hammer cup for the mark,, if you don't see a full circle transferred remove the high spots with a small dremel grinding stone,, repeat the process until the full circle of the nipple is transferred to the inside of the hammer cup.