You have to pull the rear wheel, but not hard at all once wheel off. Make sure speedo drive in hub is engaged before you tighten axle. If not speedo will quit before long. Should be about a 1/16" gap between center hub, and brake backing plate all the way around.
I replaced my rear brakes at about 87,000 miles, but how you use it, and the type of riding you do will affect the life of them. The guage on the rear hub is just a guide, to know if they are really worn out, you need to remove the wheel and look at them. I say this because even them length of the chain can make the guage read different. The next time you have to tighten your change, pay attention to your rear brake peddle, if you dont adjust the brake, the pedal will have less travel before grabbing. When I bought my bike new, the adjuster was between 1/3 and 1/2 way used with everything new. The dealer told me I could remove the lever on the rear hub and move it back 1 or 2 splines and the indicator also moves further back to the usable range and you dont have so much rod sticking out of the adjuster. A smaller sprocket on the rear will also affect how it reads.