How can I replace the siding on my garage when its on the property line, and 12" adjacent to another structure?
Seems like the best bet would be building a new wall inside the garage, on the floor. Do all the framing, and put the siding on the top. To make room for the jacks in step 2 you'd probably need to do it in 3 sections.

Then you have to support the roof while you demolish the old wall. Put a jack at each end, and 2 more evenly spaced across the span. Get beams of sufficient size to support the roof, and raise the jacks. Then tear out the old framing and siding.

Now the fun part. Stand up the newly built walls and get them around the jacks and into the right location. Attach them to the foundation, side walls and each other, then lower the roof back down and attach it.