That is an entry point to the back of the post, but not the area you need to access. You could pull the fender and cut small holes, no bigger than needd to do what you need as these are a support for your doors as well as windshield.
For the door limit s=traps use nutserts, they can be put in from the front, for the hinge plate, I have no solution other than pull the post, or cut a small acess hole right behind the offending location.