what is the easiest way to open the headlight case?
"easiest" is really relative or subjective, and it depends on whether you're trying to open the original assemblies or some aftermarket assemblies. I've never tried to open Ford's assemblies: from what I've read, they're a b*tch to work with because of the sealant they use. On aftermarket assemblies, I've tried both the oven method and the heatgun method, and I found the heatgun method easier for me, but more time consuming. Basically, I heat up a length of the assembly, about 6-8 inches at a time, and pry that portion out using a relatively wide-blade screwdriver or a putty knife (I used old chopsticks to keep it open once I pry it). Then move on the the next 6-8 inches. The advantage of doing it this way is that you can take your time and you have less chances of heat damage to the entire assembly. I use the heatgun to clean up afterwards anyway, so either way I needed a heatgun
do I need to install resistors so the the kit work fine with Auto-on light (TRS do not recomend can-bus harness for 55W nor for DRL)? and what is the proper resistor arraignment to do so?
Auto-On and DRL are 2 different beasts.
I don't have the DRL feature turned on at the SJB, so I can't answer to that. As I understarnd, DRL with our trucks don't work with HID because we have a single Low & High Beam assembly. I'm no expert there, but all the DRLs I know use the separate High Beam at a lower % of full voltage, not the Low Beam. That does not play well with the ballast.
Auto-On works just fine without resistors, however I don't like to use that feature: on overcast days, all it takes is going under a bridge and the darn things will come on for like 15 seconds and turn off. That's not good for the bulb or the ballast. I get the "light out" warning anyway, since I have LEDs in the front and rear, so I'm used to hitting reset a few times and I won't bother installing load resistors for now.