Dead set easy.
Remove lower fairings, support back of bike at frame just behind engine sump. Remove 14mm bolts which bolt shock in and drop it out the bottom.
Very, very easy. The '03 shock fits straight in, no modification neccessary.
Since this post I have had the '03 shock in my '01 completely rebuilt (resprung, screwed preload adjuster, new valve, valving setup by the guy which goes the factory yamaha team suspension, modified reservior and 5mm shorted lower linkage). I am extremely happy with the result and it cost heaps less than an ohlins or penske, and furthermore this shock is now setup exactly to MY weight which is better than an off the shelf ohlins.
Billet top clamp-custom billet damper mount-full Ti muzzy-jet kit-airbox mod-AFE filter-flow commander-ported-R1 carbon grips-carbon tach face-custom billet bar ends-gilles rearsets-custom paint-flushmounts-anodized disk centers-all suspension re-valved & resprung-rear suspension link-tinted screen-seat cowl-afam 47 rear-180/55 rear-chrome levers-chrome top/bottom clamps-braided brake lines-heat wrapped headers-xenon globes-tank bra-did I miss anything?