Good news is there are a zillion threads. Bad news is there are a zillion threads.
Is there a modding for dummies thread I haven’t found yet that a 12 year old could follow?
A zillion different lights too. Which one do you want to mod?
I started here.
Still think the best 1st project is to build a P60 drop in and put it in a P60 host!
I’d like to start with something very simple and that thread looks good 
Once I actually mod something I think the other threads here will make more sense.
Is there anything that clear for de-doming and adding resistors?
De-doming is really easy to do. Just submerge your LED/board in gasoline for a few hours. Shake it and the dome will come off. Then rinse it with water. Ready to go.
Resistor mod is more advanced though…
Lots of good links in this post
Resistor mod is probably easiest to take some detailed pics of the driver and ask the experts here. I know I can barely understand what each components is, not even mentioning what ridiculous function each component performs in conjunction with each other through the traces and whatnot.
Thanks everyone. Those are excellent references that fill in a lot of blanks for me.