This is an odd one. There is a TSB for the exhaust cam gear failure on a range of engines made up to 2009. The suggested fix is to replace with new revised cam gear. It would appear that this fix is intended to address the same issue. Possibly it has been made irrelevant by the production revision and the availability of revised cam gears.
Note the warranty procedures suggests replacing not just the cam gear but also the cam tower/tray (housing) and the camshaft. Obviously the cam gear hydraulic actuator is fed with pressurized oil through the camshaft and the cam tower so there may be some interaction here that we don't know about and some suble difference intended to improve oil flow.
Anyway, would I want an engine that someone else has monkeyed with, when there is a manufacturer fix available? Not really.
PS> In other news, JUBU tells me that the cam gears fail above 8000rpm.
I have never done it, but I have seen a Toyota training video where the 2gr-fse camshafts with gears are removed in-car. If you want a link I can probably dig it up. You hold the chain up with a elastic band to keep it from dropping. And of course use paint to mark the links to put them back correctly. I would not even attempt it in a FWD car like a Camry or HIghlander or RAV4 - with the rearward tilt of Bank 1, the access makes it pretty misreable just doing a timing belt or valve cover gasket on the earlier V6's. But it should be doable in a MR2. I doubt that the cam gear can come off in car without removing the camshaft from the engine. It is inserted about 30cmmm into the front of the camshaft.