Can I add a 12oz or 24oz of honey to a cooled 5 gallon wort without boiling it or does it have to be boiled. Does 12oz or 24 oz sound like the right addition to the wort, I was going to add 4oz of watermelon extract at bottling.
You are probably best suited to add the honey at the last half or last third of primary fermentation. This way, the yeast will have already metabolized/fermented many of the more complex sugars, such as maltose and maltriose. I would suggest boiling a few cups of water, letting it cool a bit, mix in your honey, cool the rest of the way down to your fermentation temperature, then add right into the fermenter.
Another benefit of doing it this way is since the yeast have already gone through the growth phase, bacterial contamination is unlikely, since that beer is the 'yeast gang's territory' at that point!
If you add the honey when you first pitch, they will go to work on the simple stuff first and you might be left with a sweeter beer than you would like.
Mead is often made without boiling the honey at all, so I would assume you'd be OK. I've added honey to beer with good effect twice now, but I did it after the primary malt fermentation was done. Adding the honey before you pitch will be fine, but you will loose some honey aromatics due to the vigorous primary fermentation.
I generally try to use unpasteurized honey whenever possible. Since I am shelling out for the good stuff, I don't want to apply heat because it cooks off many of the flavors. I usually mix the honey with water and then add crushed campden tablets(Potassium Metabisulphite). Just do it the night before you plan to brew.
Though the flavor nuances you gain using this technique may be hard to detect with the watermelon extract.
edit - I forgot to mention that honey itself is antibacterial. If you are using pasteurized honey you should be good to go as long as you just opened it.