I replaced them on my old mk1 GS300 without a full dismantle, although you will need to remove the disc. The main problem is if the little bolts that hold the shield to the hub ALL shear off. If only one or two do, you can sort it out as there are still enough left to hold the replacement shield in place. Take it real slow and careful getting them off - pre soak with penetrating oil etc and obviously keep oil and stuff well clear of the discs and pads. Basically, get the little retaining bolts out. Use some tin snips to cut through the old shield, with one cut on either side, you can then easily get the two halves out. In worst case scenario, you can get away without it, but it is better to have them. For the replacement, cut just one slot. You can then bend the shield open, i.e. bend each side of the cut in the opposite direction to each other, you can then wangle it around and get it in place over the hub. Bend it straight again and fit the retaining bolts. Once it is all done up, do any final bending to get the shield straight again. You do end up with a cut in the shield, but a whole lot less work than a full dismantle.