All of the above will certainly work. My technique is pretty simple, but labor intensive. It involves a lot of stitch picking. Hopefully, the original quilting was a large meander pattern!
First thing that I do is examine the quilt to see where I can sew a stabilizing line...could be SID between the quilt body and the final border, or (if no border), create my own by running a fairly tight stitched line all the way around the quilt at approx. 4" from the edge. This line is to ensure that any stitching beyond the line won't pull out once I pick out the quilting between the line and the quilt edge.
Remove binding and pick out original edge stabilizing stitches at the same time. Then, pick out the quilting all the way around, between the edge and the "new" stabilizing line I add in step 1, to give me a good 4" of working material.
Once the 3 layers are free again, isolate each layer to add whatever you need (don't forget to make the batting and backing bigger than the top, just like when it was originally made). To add more batting, I simply use a fusible interfacing along the seam to join the 2 pieces.
Then, re-load the entire quilt on the frame and quilt as normal.
Again, labor intensive, but you'll never notice that it was done, once the quilt is finished.