Thank you!
The timings are what I have the most trouble with. In this case at least, with some trial and error, I could determine when a thing had to happen so that it had the desired effect. Knowing that was only part of the solution as I couldn't find any code where this change was being done for the ability I was trying to alter. It just sort of came to me when I was digging into the debug fields.
The AC Bonus code should work at that timing on a feat just as well as on the archetype where I put it. It is just a matter of the right code at the right timing for most things.
As for your DC dilema, try looking at this
thread, it might provide some insight. You can also look for other classes or archetypes that change something similar.