I recently did this on my Canter. Certainly way more effort than getting to a CV (ie shaft out) in a IFS fourby I'm use to working.
You do have to pull off the entire hub assembly to get to it, which sucks a bit. Given this effort I'd factor replacing anything that's a little bit sus while it's apart. As I plan to start spending a few years on the road around Oz later this year, I did wheel bearings, stub axel/steering bearings, axel seals, wheel cyls, shoes, drums, brake lines, etc etc for both sides. It was done over 3 days on stands in the front yard (I was luckily on holiday's and had normal car for parts runs). If you just do the boot it will make things easier and certainly faster, I just wanted piece of mind as it's an FG434 (ie old, 1990).
With regards to crap getting in the boot, I didn't go dirt either while mine was torn. Interestingly it had Sika on it, so someone had patched it up before. You could do this if you get it clean enough and it's not that bad as they don't rotate like an IFS setup, so it only has to handle turning. Sika 252 is tough as and would work as a stop gap for a while. On the canters at least the CV housing ball at the end also has a double lipped seal that runs on it. It reminded me of how Landcruisers etc work with their setup. They have something like this as the only seal (no boot). I'm sure the Cruiser/Patrolseal is more robust and designed to cop all external elements, but still the seal on the Canter (assuming Isuzu is the same) means having a torn boot doesn't immediately expose the CV like in an IFS vehicle.
It has made me thing, the effort to do all the work was substantial and I'd be pretty pissed tearing another boot. I'm considering trying to make up a guard to deflect sticks etc. Of the axel would always leave exposed gaps due to turning, but maybe off the steering cross rod would be the go?
