I would like to replace the weather seal at the bottom of my garage door. The issue is that the bottom bracket of the door is a "wrap" around bracket (see picture). In order to slide the old seal off, I have to remove the bracket. I have watched several tutorial videos online and none of the doors seems to have this type of bracket. I figured that if open the door all the way, there's less tension on the cable connected to the bracket and that it is probably okay to do so, however, on the packaging of the replacement seal it says "at no time should you remove bottom roller carrier". The roller carrier is part of the bracket. Is it safe to remove the bracket when the door is all the way open so I can slide off the old weather seal and slide in the new one?
You're right about the tension being at a minimum when the door is up. There is tension to hold the door in that horizontal position and that tension can be considerable. What the manufacturer is also worried about is if you remove the bottom roller carriers the door will come crashing down, and they can weigh anywhere from 200 to 800 pounds. You need to support the door in the "up" position, a few "c" clamps and a few small pieces of 1x2's clamped in the roller channels so the door can't move. Do not rely on the garage door opener to hold the door in the "up" position. Then proceed to remove the bolts from the bottom brackets. You should then be able to pry the bracket away from the bottom of the door without actually removing it but freeing up the bottom track so you can install the new seal. Good luck.
Absolutely not. You are right, those pieces are under tension even when the door is up. The tension may be at "minimum" but it is still considerable. You will not be able to remove them without risk of personal injury - either from the residual spring force, or the now-undersprung door violently dropping!
Also it will be infeasible to reattach the plate while fighting the spring force. From a ladder.
The dropping can be managed by putting a vice grip on the track (I for one prefer also putting a bolt through a hole in the track, there are usually plenty)... but dealing with the spring force requires you unwind the spring force entirely using winding bars. This is garage door maintenance 203, and a good way for a novice to get hurt. You can google how to do this, but if you do, make certain that the cables are properly wound on their drums as you re-wind the spring force.
Do not under any circumswtance tamper with how the pulleys or springs attach to the shaft - you don't need to do that, it won't help, and it will be very difficult to get the door set right again if you do.
Regardless, I expect that the people who designed this weatherstripping are well aware of the hazards of messing with springs, and designed the weatherstripping to be removable without doing so. I expect if you remove the fasteners you can see, the ends will slide out of the brackets.